Hi,
fpc now supports the "type of" operator - a compile time operator which
returns the type of a variable, const, argument, property, function
result or derived types.
It is enabled in modes objfpc and extendedpascal, and can be turned on
with $modeswitch TypeInquiry.
Examples:
{$mode objfpc}
var
Int: integer;
Val: type of Int; // integer
It can be used everywhere a type is possible:
type
TInt = type of Int; // integer
function Run(a: type of Int): type of Int;
var
Arr: array of type of Int;
El: type of Arr[123]; // no range or overflow check is done
b: byte;
begin
b := type of b(Val); // type cast
b := (type of b)(Val); // type cast with brackets
end;
type-of can get function result types:
type
TFuncRes: type of Run(1); // integer
Note: The function is not called. The parameters are merely used to
figure out the right overload.
type-of can be used to get the combined type:
type
generic TSum<S,T> = record
Sum: type of (S+T); // e.g. S=double, T=single, Sum: double
end;
And the dereferenced type:
type
generic TGen<aPointerType> = record
BaseType: type of aPointerType^; // e.g. BaseType=Word for PWord
end;
Mattias
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