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delphirttitypeinfo
Enzo Costantini
Enzo Costantini

Reputation: 167

Where is the definition of "TypeIdentifier"

I would need to write a function that performs operations in RTTI mode on data, of which I do not know a priori the type. I tried to write a function like this:

function doSomething (T: TypeIdentifier): Boolean;

as when using the expression TypeInfo(T) he expects as a type parameter TypeIdentifier see the snapshot

But when I try to compile I get an error because the type TypeIdentifier not recognized.
Someone could explain me how I can do to send a data type of which I know the type only at runtime?
Thanks to the availability.
Enzo

Upvotes: 3

Views: 908

Answers (1)

David Heffernan
David Heffernan

Reputation: 613461

TypeInfo is an intrinsic function that uses compiler magic. That is the compiler generates the code that implements the function rather than it being part of the runtime library.

You don't have access to such magic. You cannot create a function that accepts a type identifier in the manner of TypeInfo. So you need to make your function accept what TypeInfo returns, a pointer to the type info, PTypeInfo.

You'd call your function like this:

DoSomething(TypeInfo(SomeTypeIdentifier));

Now technically, you may notice that TypeInfo returns a value of type Pointer. That's because PTypeInfo is defined in another unit, TypInfo and the System unit where all intrinsics are defined is not allowed to use TypInfo. But as stated in the documentation linked above, TypeInfo returns a pointer to TTypeInfo.

Upvotes: 3

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