What is Delphi's equivalent to "+=" for adding elements to a set?

Question

In other languages like C++, there are operators to do a plus-equals or or-equals type of operation to add additional styles/flags. Is there an equivalent in Delphi?

Right now I have some code like:

label1.Font.Style := label1.Font.Style + [fsBold];
label2.Font.Style := label2.Font.Style + [fsBold];

But I would love, if it is possible, to get that simplified a bit to something more concise without duplicating the label name on both sides of the assignment operator, something along the lines of: label1.Font.Style += [fsBold]; or label1.Font.Style := self + [fsBold];

Can this be done? Or not so much?

Fundy

use the 'inc' function - docwiki.embarcadero.com/Libraries/en/System.Inc. Anyway you can not use it on properties. – Marshy

For sets, it wouldn't be Inc, it would be the Include procedure with the same problem that it requires a variable. – Choragus

For strings, use Concat(S1, S2, S3, S4...) – Thimbu

No, @Jerry, that function doesn't work that way. It doesn't modify any of its arguments, unlike Inc and Include. Furthermore, Concat is no different from the more idiomatic use of repeated + operators. (The function used to be more efficient for four or more operands, but that changed around version 5, maybe earlier.) – Gibby

Answer 1

This is one of the few cases where I can recommend the with statement:

with label1.Font do Style := Style + [fsBold];
with label2.Font do Style := Style + [fsBold];

Normally, the problem with with is that it is unclear what's a member access and what isn't, but if the scope is a single statement in which a single property is used, it's clear enough.

Choragus

What happens when with label2.Font do Style := Style + [fsBold]; is executed repeatedly? – Telegraphic

what you gain is that label.Font isn't resolved twice there – Craft

Answer 2

Include is what you're looking for. Unfortunately you run into the problem that Label.Font.Style is a property and must be assigned to and not passed by var. You can do this however:

var
  fontStyle: TFontStyles;
begin
  fontStyle := Label1.Font.Style;
  Include(fontStyle, fsBold);
  Label1.Font.Style := fontStyle;

Osculum

Answer 3

Delphi has the Inc function, but it does not work on properties:

Inc(a);     // Increment a with 1
Inc(a, 5);  // Increment a with 5

If you need to add style to a font often, you can write a procedure:

procedure AddStyle(const AFont: TFont; const AStyle: TFontStyles);
begin
  AFont.Style := AFont.Style + AStyle;
end;

(With later versions of Delphi you can use class helpers).

Valency

+1, And I just fix your AddStyle method :), also you can add a sanple of use like so AddStyle(Label1.Font, [fsBold]); – Fleck

Answer 4

Subclass TLabel type and create a method like this:

procedure TMyLabel.AddStyle(const AStyle: TFontStyles);
begin
 Self.Font.Style := Self.Font.Style + AStyle;
end;

Then you can put the class into a bpl package and install it into editor. After that, you can replace all your labels to your customized labels. For large project i would recommend Notepad++ to replace all your declarations in .pas and (text!) .dfm files. This may sound complicated but it's less than an hour of work. Good luck!

Pedate

dont do this, the complexy you introduce to the code is far then worth the extra work. do it in a visitor pattern, (create an external function that accept TLabel and TFontStyles and do the work in a function). – Lamontlamontagne

This is probably one of the worst possible reasons to create a subclass. A simple utility function does the job quite nicely, without interfering with your class hierarchy. – St