What is the difference between statically typed and dynamically typed languages?

Question

What does it mean when we say a language is dynamically typed versus statically typed?

Cookshop

@EricLeschinski I think unit tests help now with that problem and dynamically typed languages such as JavaScript can be coded with reassurance that it will hold up, thus making it eligible for enterprise software development, wouldn't you think? – Reimers

At best, those unit tests deteriorate with time and get turned off by co-workers trying to increase job security, at worst, they never get written in the first place. It's like suggesting to a pro mechanic to use duct tape on his customer's cars. Yes junior, using duct tape on this transmission job is a good idea... for you. – Birl

android.jlelse.eu/… might be useful too – Sinus

Answer 1

Statically typed languages

A language is statically typed if the type of a variable is known at compile time. For some languages this means that you as the programmer must specify what type each variable is; other languages (e.g.: Java, C, C++) offer some form of type inference, the capability of the type system to deduce the type of a variable (e.g.: OCaml, Haskell, Scala, Kotlin).

The main advantage here is that all kinds of checking can be done by the compiler, and therefore a lot of trivial bugs are caught at a very early stage.

Examples: C, C++, Java, Rust, Go, Scala

Dynamically typed languages

A language is dynamically typed if the type is associated with run-time values, and not named variables/fields/etc. This means that you as a programmer can write a little quicker because you do not have to specify types every time (unless using a statically-typed language with type inference).

Examples: Perl, Ruby, Python, PHP, JavaScript, Erlang

Most scripting languages have this feature as there is no compiler to do static type-checking anyway, but you may find yourself searching for a bug that is due to the interpreter misinterpreting the type of a variable. Luckily, scripts tend to be small so bugs have not so many places to hide.

Most dynamically typed languages do allow you to provide type information, but do not require it. One language that is currently being developed, Rascal, takes a hybrid approach allowing dynamic typing within functions but enforcing static typing for the function signature.

Muhammadan

Type inference is mostly a feature of dynamically typed languages, but can and is used in some statically typed languages as well. I did not intend to be categorical in the sentence you quoted, it is just an observation of a common (but not exclusive) consequence of static typing. – Muhammadan

@Muhammadan Can you name any dynamically typed language which implements HM type inference? – Cornerwise

"A language is dynamically typed if the type of a variable is interpreted at runtime": No. A language is dynamically typed if the type is associated with run-time values, and not named variables/fields/etc. – Interwork

@Paul Biggar: Ah, I see the subtle difference, but it comes down to the same thing doesn't it? I can't think of an example where it doesn't. – Muhammadan

"HM type inference" is "Hindley–Milner type inference"; see en.wikipedia.org/wiki/Type_inference What dynamically typed languages do is not usually called type inference. – Boxer

Incorrect, static typing means "that a reference value is manifestly (which is not the same as at compile time) constrained with respect to the type of the value it can denote, and that the language implementation, whether it is a compiler or an interpreter, both enforces and uses these constraints as much as possible." cited from : c2.com/cgi/wiki?StaticTyping which, how I understand it, is correct. – Gewgaw

@Muhammadan -1 "This in practice means that you as the programmer must specify what type each variable is...This means that you as a programmer can write a little quicker because you do not have to specify type everytime". C# has var, C++ has auto and all languages descended from the ML family (late 1970s, e.g. Standard ML, OCaml, Haskell, F#) have full Hindley-Milner type inference so you don't annotate any types. So your statements are totally factually incorrect. – Tosspot

It's probably worth mentioning that dynamically-typed languages often have little enforcement of the arguments that get passed to a function, or the expected members of an object. This can allow for some speedily-constructed code in a dynamically-typed language, but the down-side is that some bugs can only be discovered at run time, when an expected member is not present, or an argument to a function is missing or out of order. – Togo

The thing most obvious about the type systems of Java, C, C++, Pascal, and many other widely-used “industry” languages is not that they are statically typed, but that they are explicitly typed.In other words, they require lots of type declarations. (In the world of less explicitly typed languages, where these declarations are optional, they are often called “type annotations”.) This has nothing to do with static types. continued.. – Derrik

The first statically typed languages were explicitly typed by necessity. However, type inference algorithms – techniques for looking at source code with no type declarations at all, and deciding what the types of its variables are have existed for many years now. The ML language, which uses it. Haskell, which improves on it, is now about 15 years old. Even C# is now adopting the idea, which will raise a lot of eyebrows and undoubtedly give rise to claims of its being “weakly typed”. continued... – Derrik

If one does not like type declarations, one is better off describing that accurately as not liking explicit types, rather than static types. Source cdsmith.wordpress.com/2011/01/09/an-old-article-i-wrote – Derrik

you wrote "... interpreter misinterpreting the type of a variable." but you must mean "... the coder misinterpreting the type of a variable." :) – Solander

@MattWolf , In your comment You have mentioned "reference value" is there a reason for using the keyword or for my understanding I can replace it with "Variable Value". Cause for programmers like me having C# background we get confused as there are 3 basic types "Value Types", "Reference Types" and "Pointer Types" supported by the language. And if You indeed mean "reference value" can You shed some light on what do You mean by "reference value". – Derrik

Note that C++, C# and Java all have either auto(C++) or var (C#/Java) which provides type inference. – Ambagious

any Flutter/dart peeps coming here, yes dart is statically typed :), though it allows us to implicitly create a dynamic variable by specifying dynamic dart.dev/faq – Siebert

Are statically typed languages same as strongly typed languages? – Gaul

I don't actually agree with this answer. Notice, that you could take any Java code, and replace any declaration type with Object. You can't call methods anymore, so before any method call and field access proper casting would be required, in which case you can achieve dynamic typing in Java (albeit cumberstone, because of the numerous casts). The type would be resolved at runtime, just like python or JS. The difference is whether the language allows you to call method with or without casting. – Pickmeup

Answer 2

Type checking is the process of verifying and enforcing the constraints of types.

• Statically typed programming languages do type checking at compile-time.
  Examples: Java, C, C++.

• Dynamically typed programming languages do type checking at run-time.
  Examples: Perl, Ruby, Python, PHP, JavaScript.

Tetrachord

I think this is the best answer. In particular, the accepted answer is largely factually incorrect. – Tosspot

@JonHarrop In what ways specifically? – Sayer

@thomas: "This means that you as a programmer can write a little quicker because you do not have to specify type everytime". You do not have to specify the type every time with static typing if you have type inference. See SML, OCaml, F#, Haskell... – Tosspot

In statically typed prog languages the type checking is done before runtime, but not exactly at compile time. – Erection

Let me confuse you more: As of Java 10, the var keyword has been introduced, to give Java developers a taste of dynamic typing, but Java is still statically typed. – Margrettmarguerie

@Margrettmarguerie I think you are confusing dynamic typing with type inference. With var you tell the compiler, 'please deduce the type for me'. The program is then compile exactly as if you wrote that specific type. The compiler will issue type errors when the variable is used incorrectly. Dynamic typing means that the type is only known at runtime (and actually not associated with the variable), as the answer by NomeN points out. This is of course totally not the case with Java. – Estrin

Answer 3

Here is an example contrasting how Python (dynamically typed) and Go (statically typed) handle a type error:

def silly(a):
    if a > 0:
        print 'Hi'
    else:
        print 5 + '3'

Python does type checking at run time, and therefore:

silly(2)

Runs perfectly fine, and produces the expected output Hi. Error is only raised if the problematic line is hit:

silly(-1)

Produces

TypeError: unsupported operand type(s) for +: 'int' and 'str'

because the relevant line was actually executed.

Go on the other hand does type-checking at compile time:

package main

import ("fmt"
)

func silly(a int) {
    if (a > 0) {
        fmt.Println("Hi")
    } else {
        fmt.Println("3" + 5)
    }
}

func main() {
    silly(2)
}

The above will not compile, with the following error:

invalid operation: "3" + 5 (mismatched types string and int)

Ivon

Thanks for the tidy example. So I infer that all of the scripting languages are Dynamically typed, as they are not compiled? – Embolism

yes. all scripting languages are dynamically typed, because their is no compiler to do static type checking anyway. This point has been illustrated in this article sitepoint.com/typing-versus-dynamic-typing . – Reeducate

Scala can be used as scripting language and it is statically typed! #discussion @Reeducate – Lx

@Reeducate Compilation doesn't mean statically-typed. Haskell can be interpreted with runhaskell, for example. – Romito

Also Scripting language does NOT mean interpreted language. TypeScript is statically typed, compiled/transpiled, but scripting language. – Waggon

A "piece of code" is worth a thousand words. All the verbosity in the previous answers didn't light the bulb in my head the way this piece of code did. And now that that verbosity makes absolutely perfect sense :) Many Thanks. – Poetry

Smart precise answer. – Myocardiograph

Why is this not accepted as an answer? So simple yet so verbal. – Platoon

Best answer, +1 – Bravura

This should be accepted as the best answer. Not that the currently accepted is wrong but reading this I had an "aha!" moment. – Kronos

I've added an answer below which dissects this example further. showing that the fact that python is interpreted and go is compiled has no effect on the type-checking/errors. let me know what you think! – Shellbark

@CᴴᴀZ It's not that simple. Python is not a pure interpreted language, it runs an optimising compiler that produces interpreted byte-code. And as many have already mentioned, being interpreted has little to do with being dynamically typed. It's is a design choice. Static languages provide far less flexibility offering enhanced optimisation and error-tracking capacity in return. Yet, some things are notoriously hard to express with static typing (e.g. functional programming: Haskell and Scala utilise unbelievably sophisticated type systems to make static FP expressive and efficient). – Multiangular

True @EliKorvigo . Out of curiosity, can we a statically-typed language which is 100% interpret-able? – Embolism

@CᴴᴀZ Sure, you can. – Multiangular

@CᴴᴀZ: Compilation and interpretation are traits of the compiler or interpreter (duh!) not the language. Every language can be implemented by an interpreter and every language can be implemented by a compiler. I think you are confused by the fact that almost all answers to this question claim that "static typing" means "type checking at compile time" and "dynamic typing" means "type checking at runtime". That is wrong. To be 100% correct, it should be "static typing" means "type checking before runtime". Gofer was a (now defunct) dialect of Haskell that was implemented by an interpreter. … – Coacervate

… Also, there are interpreters for C and C++. On the other hand, all current mainstream implementations of ECMAScript, PHP, Python, and Ruby have compilers. Some of them even more than one. – Coacervate

Answer 4

Simply put it this way: in a statically typed language variables' types are static, meaning once you set a variable to a type, you cannot change it. That is because typing is associated with the variable rather than the value it refers to.

For example in Java:

String str = "Hello";  // variable str statically typed as string
str = 5;               // would throw an error since str is
                       // supposed to be a string only

Where on the other hand: in a dynamically typed language variables' types are dynamic, meaning after you set a variable to a type, you CAN change it. That is because typing is associated with the value it assumes rather than the variable itself.

For example in Python:

some_str = "Hello"  # variable some_str is linked to a string value
some_str = 5        # now it is linked to an integer value; perfectly OK

So, it is best to think of variables in dynamically typed languages as just generic pointers to typed values.

To sum up, type describes (or should have described) the variables in the language rather than the language itself. It could have been better used as a language with statically typed variables versus a language with dynamically typed variables IMHO.

Statically typed languages are generally compiled languages, thus, the compilers check the types (make perfect sense right? as types are not allowed to be changed later on at run time).

Dynamically typed languages are generally interpreted, thus type checking (if any) happens at run time when they are used. This of course brings some performance cost, and is one of the reasons dynamic languages (e.g., python, ruby, php) do not scale as good as the typed ones (java, c#, etc.). From another perspective, statically typed languages have more of a start-up cost: makes you usually write more code, harder code. But that pays later off.

The good thing is both sides are borrowing features from the other side. Typed languages are incorporating more dynamic features, e.g., generics and dynamic libraries in c#, and dynamic languages are including more type checking, e.g., type annotations in python, or HACK variant of PHP, which are usually not core to the language and usable on demand.

When it comes to technology selection, neither side has an intrinsic superiority over the other. It is just a matter of preference whether you want more control to begin with or flexibility. just pick the right tool for the job, and make sure to check what is available in terms of the opposite before considering a switch.

Strobel

This makes a lot of sense. I think it explains at least the reasoning behind the names much better than other answers here. – Hoy

According to this reference Python is both a statically typed and dynamically typed language: wiki.python.org/moin/… Does anyone know why? – Osteen

Lucas, To the contrary the document keeps iterating that Python is both strongly and dynamically typed. Where did you see that? Can you quote? – Strobel

I think this answer best communicates the the concept in the simplest fashion. A lot of other answers try to abstractly describe the concept, but fail at some detail. I would rather see this answer at the top of the list. – Jungian

Most other answers created more questions in my mind. This one cleared all of them. This answer really should be at the top IMHO – Ling

"To sum up, type describes (or should have described) the variables in the language rather than the language itself."..What about Kotlin? – Vitek

I think the word "typed" prevents clarity. Your answer cleared it up for me :) Every time I have heard this in the past, I was thinking of typing on a keyboard, like having something to do with the way in which you declare or don't declare variables; data-types NEVER crossed my mind. So "Typed" refers to the ability of datatype of the variable to change state, whether the datatype of the variable is static or dynamic. Ex. Dynamic (Str -> int -> Boolean) – Ryle

@GvSharma: Kotlin transpiles Java code to JavaScript; so both languages (or the state of the code in each of them) must be considered separately, I think. – Strobel

@Osteen That page says strongly typed not statically typed. – Sententious

@KorayTugay Ah, thank you for the note! I think I misunderstood that first sentence People often use the term strongly-typed language to refer to a language that is both statically typed and strongly-typed and thought that they meant that Python was statically typed. But that makes no sense, and I see how they mean to say that Python is strongly typed :) – Osteen

I think there is some inconsistency in your answer. First "in a statically typed language variables' types are static, meaning once you set a variable to a type, you cannot change it". Then "Statically typed languages are generally compiled languages, thus, the compilers check the types". These are not the same thing. Suppose, that python didn't allow to change the type of a variable (runtime, if it encounters that there is a type change, it would generate an exception). With your first definition, this would make python a statically typed language. But still dynamically typed with the second. – Iggie

Answer 5

http://en.wikipedia.org/wiki/Type_system

Static typing

A programming language is said to use static typing when type checking is performed during compile-time as opposed to run-time. In static typing, types are associated with variables not values. Statically typed languages include Ada, C, C++, C#, JADE, Java, Fortran, Haskell, ML, Pascal, Perl (with respect to distinguishing scalars, arrays, hashes and subroutines) and Scala. Static typing is a limited form of program verification (see type safety): accordingly, it allows many type errors to be caught early in the development cycle. Static type checkers evaluate only the type information that can be determined at compile time, but are able to verify that the checked conditions hold for all possible executions of the program, which eliminates the need to repeat type checks every time the program is executed. Program execution may also be made more efficient (i.e. faster or taking reduced memory) by omitting runtime type checks and enabling other optimizations.

Because they evaluate type information during compilation, and therefore lack type information that is only available at run-time, static type checkers are conservative. They will reject some programs that may be well-behaved at run-time, but that cannot be statically determined to be well-typed. For example, even if an expression always evaluates to true at run-time, a program containing the code

if <complex test> then 42 else <type error>

will be rejected as ill-typed, because a static analysis cannot determine that the else branch won't be taken.[1] The conservative behaviour of static type checkers is advantageous when evaluates to false infrequently: A static type checker can detect type errors in rarely used code paths. Without static type checking, even code coverage tests with 100% code coverage may be unable to find such type errors. Code coverage tests may fail to detect such type errors because the combination of all places where values are created and all places where a certain value is used must be taken into account.

The most widely used statically typed languages are not formally type safe. They have "loopholes" in the programming language specification enabling programmers to write code that circumvents the verification performed by a static type checker and so address a wider range of problems. For example, Java and most C-style languages have type punning, and Haskell has such features as unsafePerformIO: such operations may be unsafe at runtime, in that they can cause unwanted behaviour due to incorrect typing of values when the program runs.

Dynamic typing

A programming language is said to be dynamically typed, or just 'dynamic', when the majority of its type checking is performed at run-time as opposed to at compile-time. In dynamic typing, types are associated with values not variables. Dynamically typed languages include Groovy, JavaScript, Lisp, Lua, Objective-C, Perl (with respect to user-defined types but not built-in types), PHP, Prolog, Python, Ruby, Smalltalk and Tcl. Compared to static typing, dynamic typing can be more flexible (e.g. by allowing programs to generate types and functionality based on run-time data), though at the expense of fewer a priori guarantees. This is because a dynamically typed language accepts and attempts to execute some programs which may be ruled as invalid by a static type checker.

Dynamic typing may result in runtime type errors—that is, at runtime, a value may have an unexpected type, and an operation nonsensical for that type is applied. This operation may occur long after the place where the programming mistake was made—that is, the place where the wrong type of data passed into a place it should not have. This makes the bug difficult to locate.

Dynamically typed language systems, compared to their statically typed cousins, make fewer "compile-time" checks on the source code (but will check, for example, that the program is syntactically correct). Run-time checks can potentially be more sophisticated, since they can use dynamic information as well as any information that was present during compilation. On the other hand, runtime checks only assert that conditions hold in a particular execution of the program, and these checks are repeated for every execution of the program.

Development in dynamically typed languages is often supported by programming practices such as unit testing. Testing is a key practice in professional software development, and is particularly important in dynamically typed languages. In practice, the testing done to ensure correct program operation can detect a much wider range of errors than static type-checking, but conversely cannot search as comprehensively for the errors that both testing and static type checking are able to detect. Testing can be incorporated into the software build cycle, in which case it can be thought of as a "compile-time" check, in that the program user will not have to manually run such tests.

References

1. Pierce, Benjamin (2002). Types and Programming Languages. MIT Press. ISBN 0-262-16209-1.

Germann

It just seemed redundant since it's a link to wikipedia and not some transient website, but I'll remember that next time. – Germann

somehow I still cannot think of an example in a dynamically typed language where a type is not clear at compile time but must be figured out at runtime. Could you provide me with some? – Joinville

@Joinville Old comment but imagine a scenario where some data is picked up from a remote server then that data is used to pick a property off of an object. Ex: myObject[remoteDataName]. Then there's no way of knowing which property it will pick or even if it's a valid property at all. – Salisbury

Answer 6

Compiled vs. Interpreted

"When source code is translated"

• Source Code: Original code (usually typed by a human into a computer)
• Translation: Converting source code into something a computer can read (i.e. machine code)
• Run-Time: Period when program is executing commands (after compilation, if compiled)
• Compiled Language: Code translated before run-time
• Interpreted Language: Code translated on the fly, during execution

---

Typing

"When types are checked"

5 + '3' is an example of a type error in strongly typed languages such as Go and Python, because they don't allow for "type coercion" -> the ability for a value to change type in certain contexts such as merging two types. Weakly typed languages, such as JavaScript, won't throw a type error (results in '53').

• Static: Types checked before run-time
• Dynamic: Types checked on the fly, during execution

---

The definitions of "Static & Compiled" and "Dynamic & Interpreted" are quite similar...but remember it's "when types are checked" vs. "when source code is translated".

You'll get the same type errors irrespective of whether the language is compiled or interpreted! You need to separate these terms conceptually.

---

Python Example

Dynamic, Interpreted

def silly(a):
    if a > 0:
        print 'Hi'
    else:
        print 5 + '3'

silly(2)

Because Python is both interpreted and dynamically typed, it only translates and type-checks code it's executing on. The else block never executes, so 5 + '3' is never even looked at!

What if it was statically typed?

A type error would be thrown before the code is even run. It still performs type-checking before run-time even though it is interpreted.

What if it was compiled?

The else block would be translated/looked at before run-time, but because it's dynamically typed it wouldn't throw an error! Dynamically typed languages don't check types until execution, and that line never executes.

---

Go Example

Static, Compiled

package main

import ("fmt"
)

func silly(a int) {
  if (a > 0) {
      fmt.Println("Hi")
  } else {
      fmt.Println("3" + 5)
  }
}

func main() {
  silly(2)
}

The types are checked before running (static) and the type error is immediately caught! The types would still be checked before run-time if it was interpreted, having the same result. If it was dynamic, it wouldn't throw any errors even though the code would be looked at during compilation.

---

Performance

A compiled language will have better performance at run-time if it's statically typed (vs. dynamically); knowledge of types allows for machine code optimization.

Statically typed languages have better performance at run-time intrinsically due to not needing to check types dynamically while executing (it checks before running).

Similarly, compiled languages are faster at run time as the code has already been translated instead of needing to "interpret"/translate it on the fly.

Note that both compiled and statically typed languages will have a delay before running for translation and type-checking, respectively.

---

More Differences

Static typing catches errors early, instead of finding them during execution (especially useful for long programs). It's more "strict" in that it won't allow for type errors anywhere in your program and often prevents variables from changing types, which further defends against unintended errors.

num = 2
num = '3' // ERROR

Dynamic typing is more flexible, which some appreciate. It typically allows for variables to change types, which can result in unexpected errors.

Shellbark

"Because Python is both interpreted and dynamically typed, it only translates and type-checks code it's executing on" – that's not really the case. Python (at least the reference implementation) compiles all your code at import time (you can also compile modules before/without importing them). The compiler introduces various optimisations (at least as far as Python's dynamic nature allows). – Multiangular

Answer 7

The terminology "dynamically typed" is unfortunately misleading. All languages are statically typed, and types are properties of expressions (not of values as some think). However, some languages have only one type. These are called uni-typed languages. One example of such a language is the untyped lambda calculus.

In the untyped lambda calculus, all terms are lambda terms, and the only operation that can be performed on a term is applying it to another term. Hence all operations always result in either infinite recursion or a lambda term, but never signal an error.

However, were we to augment the untyped lambda calculus with primitive numbers and arithmetic operations, then we could perform nonsensical operations, such adding two lambda terms together: (λx.x) + (λy.y). One could argue that the only sane thing to do is to signal an error when this happens, but to be able to do this, each value has to be tagged with an indicator that indicates whether the term is a lambda term or a number. The addition operator will then check that indeed both arguments are tagged as numbers, and if they aren't, signal an error. Note that these tags are not types, because types are properties of programs, not of values produced by those programs.

A uni-typed language that does this is called dynamically typed.

Languages such as JavaScript, Python, and Ruby are all uni-typed. Again, the typeof operator in JavaScript and the type function in Python have misleading names; they return the tags associated with the operands, not their types. Similarly, dynamic_cast in C++ and instanceof in Java do not do type checks.

Electrophilic

imagine answering the question with a response that makes us ask ten more questions... – Surmullet

Answer 8

In programming, Data Type is a Classification which tells us 1) what type of value a variable will hold and 2) which mathematical, relational and logical operations can be done on those values without getting an error.

When people mention "type" in the following contexts, they mean "data types".

In each programming language, to minimize the chance of getting an error, type checking is done either before or during program execution. Depending on the Timing of Type Checking, there are two types of programming languages: Statically Typed and Dynamically Typed languages (or mixed, where the user says which to use (static/dynamic) for each variable).

Also, depending on whether Implicit Type Conversion happens or not, there are two types of programming languages: Strongly Typed and Weakly Typed languages.

Statically Typed :

• Type checking is done at compile time

• In source code, at the time of variable declaration (the time when a value is assigned to a new variable), the data type of that variable must be explicitly specified (i.e., cannot be implicit/inferred/guessed) because, if the data type is specified in source code, then at compile time that source code will be converted to machine code and allow type checking to happen

• Here, data type is associated with the variable (the variable name, not the value) like, int count. This association is static (fixed)

• If we try to change the data type of an already declared variable (int count) by assigning a value of a different data type (int count = "Hello") into it, then we will get an error

• If we try to change the data type by redeclaring an already declared variable (int count) using a different data type (boolean count) then we will also get an error

int count;         /* count is int type, association between data type
                      and variable is static or fixed */

count = 10;        // no error 
count = 'Hello';   // error 
boolean count;     // error 

• As type checking and type error detection are done at compile time, no further type checking is needed during runtime. Thus, the program becomes more optimized, resulting in faster execution

• If we want more type-rigid code, then choosing this type of language is better option

• Examples: Java, C, C++, Go, Swift, etc.

Dynamically Typed :

• Type checking is done at runtime

• In source code, at the time of variable declaration, there is no need to explicitly specify the data type of that variable. Because type checking is done during runtime, the language's system determines variable type from the data type of the assigned value of that variable

• Here, data type is associated with the value assigned to the variable. For example, var foo = 10: 10 is a Number so now foo is of Number data type. But this association is dynamic (flexible)

• we can easily change data type of an already declared variable (var foo = 10), by assigning a value of a different data type (foo = "Hi") into it, not producing an error

• we can easily change data type of an already declared variable (var foo = 10), by redeclaring it using value of other data type (var foo = true), not producing an error

var foo;            // without assigned value, variable holds undefined data type 

var foo = 10;       // foo is Number type now, association between data 
                    // type and value is dynamic / flexible 
foo = 'Hi';         // foo is String type now, no error 
var foo = true;     // foo is Boolean type now, no error 

• As type checking and type error detection is done at runtime, a dynamically typed program is less optimized, results in slower execution. Although execution of these type of languages can be faster if they implement JIT (Just In Time) Compiler

• If we want to write and execute code easily, then this type of language is the better option, but here we can still unfortunately get a runtime error

• Examples : Python, JavaScript, PHP, Ruby etc.

Subfloor

Answer 9

Statically typed languages: each variable and expression is already known at compile time.

(int a; a can take only integer type values at runtime)

Examples: C, C++, Java

Dynamically typed languages: variables can receive different values at runtime and their type is defined at run time.

(var a; a can take any kind of values at runtime)

Examples: Ruby, Python.

Dittography

Answer 10

Statically typed languages type-check at compile time and the type can NOT change. (Don't get cute with type-casting comments, a new variable/reference is created).

Dynamically typed languages type-check at run-time and the type of an variable CAN be changed at run-time.

Savor

Answer 11

Sweet and simple definitions, but fitting the need: Statically typed languages binds the type to a variable for its entire scope (Seg: SCALA) Dynamically typed languages bind the type to the actual value referenced by a variable.

Antihistamine

Answer 12

Static Type: Type checking performed at compile time.

What actually mean by static type language:

• type of a variable must be specified
• a variable can reference only a particular type of object*
• type check for the value will be performed at the compile time and any type checking will be reported at that time
• size of a variable is computed at compile time

Example of static type language are C, C++, Java.

Dynamic Type: Type checking performed at runtime.

What actually mean by dynamic type language:

• no need to specify type of the variable
• same variable can reference to different type of objects

Python, Ruby are examples of dynamic type language.

Note that regardless of static or dynamic type, memory allocation for variables is performed when an app/program executed (loaded into the memory)

---

_{* Some objects can be assigned to different type of variables by typecasting it (a very common practice in languages like C and C++)}

Nonreturnable

Answer 13

• In a statically typed language, a variable is associated with a type which is known at compile time, and that type remains unchanged throughout the execution of a program. Equivalently, the variable can only be assigned a value which is an instance of the known/specified type.
• In a dynamically typed language, a variable has no type, and its value during execution can be anything of any shape and form.

Phosphoprotein

Answer 14

Static typed languages (compiler resolves method calls and compile references):

• usually better performance
• faster compile error feedback
• better IDE support
• not suited for working with undefined data formats
• harder to start a development when model is not defined when
• longer compilation time
• in many cases requires to write more code

Dynamic typed languages (decisions taken in running program):

• lower performance
• faster development
• some bugs might be detected only later in run-time
• good for undefined data formats (meta programming)

Argenteuil

Answer 15

Statically typed languages like C++, Java and Dynamically typed languages like Python differ only in terms of the execution of the type of the variable. Statically typed languages have static data type for the variable, here the data type is checked during compiling so debugging is much simpler...whereas Dynamically typed languages don't do the same, the data type is checked which executing the program and hence the debugging is bit difficult.

Moreover they have a very small difference and can be related with strongly typed and weakly typed languages. A strongly typed language doesn't allow you to use one type as another eg. C and C++ ...whereas weakly typed languages allow eg.python

Arluene

Answer 16

Statically Typed

The types are checked before run-time so mistakes can be caught earlier.

Examples = c++

Dynamically Typed

The types are checked during execution.

Examples = Python

Polychrome

This doesn't really add anything that's not yet covered by other answers, does it? – Armyworm

Yes, but most answers weren't very clear so I wanted an answer that was easy to understand. – Polychrome

Answer 17

Dynamically typed programming that allows the program to change the type of the variable at runtime.

dynamic typing languages : Perl, Ruby, Python, PHP, JavaScript, Erlang

Statically typed, means if you try to store a string in an integer variable, it would not accept it.

Statically typed languages :C, C++, Java, Rust, Go, Scala, Dart

Reaganreagen

Please always embed code as text in the post, not as screenshot images. Also, what does this answer add over previous ones? It actually has some problems: 1. it is possible for a language to be statically typed but still allow something like your Python example: a number could be cast to a string by reading it as a decimal representation, not to mention that in e.g. C a string variable is just a pointer, which a weak type system may allow treating as an int. 2. in functional programming (in the narrow sense) you don't change variables at all, but still a language may be dynamic. – Enceinte

Answer 18

dynamically typed language helps to quickly prototype algorithm concepts without the overhead of about thinking what variable types need to be used (which is a necessity in statically typed language).

Spatz

Answer 19

Static Typing: The languages such as Java and Scala are static typed.

The variables have to be defined and initialized before they are used in a code.

for ex. int x; x = 10;

System.out.println(x);

Dynamic Typing: Perl is an dynamic typed language.

Variables need not be initialized before they are used in code.

y=10; use this variable in the later part of code

Festival

Well, this answer is not completely right. In both languages, the variables must be intialized before they are used. However, in dynamically typed languages, you may choose to leave out the type where it is used. – Waive

It looks like you are misusing the term "variables", you should have said "types" instead. – Matildamatilde

I'd argue that Perl is statically typed: It has 3 types, scalar ($), array (@) and hash (%). The type of a variable in Perl is known at compile time and stays the same for the rest of the variables lifetime. – Carotid