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I'm learning Delphi myself.. I have seen the auto variable type that can do some degree of magic in C++. Is there an auto a variable type, or something similar to this, in Delphi?

Remy Lebeau
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jimsweb
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    In Delphi 10.3 and later, you can simply write `var a := RHS`; the type of `a` will be the type of the right-hand side. – Andreas Rejbrand Mar 31 '22 at 13:30
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    With that said, the use cases for `var` in Delphi are not as extensive [as those for C++](https://stackoverflow.com/q/6434971/327083) - prefer using explicit types unless you have a **very** compelling reason not to. – J... Mar 31 '22 at 14:17
  • https://www.embarcadero.com/resources/white-papers – Delphi Coder Mar 31 '22 at 15:55

1 Answers1

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auto in C++ is used to let the compiler infer a variable's data type based on what type of value is used to initialize it.

In Delphi 10.3 and later, type inference is available only on an inline variable:

Additionally, the compiler can now in several circumstances infer the type of a variable at its inline declaration location, by looking to the type of the value assigned to it.

procedure Test;
begin
  var I := 22;
  ShowMessage (I.ToString);
end;

The type of the r-value expression (that is, what comes after the :=) is analyzed to determine the type of the variable. Some of the data types are “expanded” to a larger type, as in the case above where the numeric value 22 (a ShortInt) is expanded to Integer. As a general rule, if the right hand expression type is an integral type and smaller than 32 bits, the variable will be declared as a 32-bit Integer. You can use an explicit type if you want a specific, smaller, numeric type.

Remy Lebeau
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