问题
I want some way to write a function in delphi like the following
procedure Foo<T>;
begin
if T = String then
begin
//Do something
end;
if T = Double then
begin
//Do something else
end;
end;
ie: I want to be able to do different things based on a generic type
I've tried using TypeInfo
in System
but this seems to be suited to objects rather than generic types.
I'm not even sure this is possible in pascal
回答1:
TypeInfo should work:
type
TTest = class
class procedure Foo<T>;
end;
class procedure TTest.Foo<T>;
begin
if TypeInfo(T) = TypeInfo(string) then
Writeln('string')
else if TypeInfo(T) = TypeInfo(Double) then
Writeln('Double')
else
Writeln(PTypeInfo(TypeInfo(T))^.Name);
end;
procedure Main;
begin
TTest.Foo<string>;
TTest.Foo<Double>;
TTest.Foo<Single>;
end;
回答2:
From XE7 onwards you can use GetTypeKind to find the type kind:
case GetTypeKind(T) of
tkUString:
....
tkFloat:
....
....
end;
Of course tkFloat
identifies all floating point types so you might also test SizeOf(T) = SizeOf(double)
.
Older versions of Delphi do not have the GetTypeKind
intrinsic and you have to use PTypeInfo(TypeInfo(T)).Kind
instead. The advantage of GetTypeKind
is that the compiler is able to evaluate it and optimise away branches that can be proven not to be selected.
All of this rather defeats the purpose of generics though and one wonders if your problem has a better solution.
来源:https://stackoverflow.com/questions/31042997/testing-the-type-of-a-generic-in-delphi