Delphi Generics: Can array types be used as type constraints?

Question

I have the following code that doesn't compile, and I can't find an explanation as to why.

TIndexArray<TType> = array of TType;

TIndexList<TArrayType; TType: TIndexArray<TArrayType>> = class
end;

It says the

Type 'TIndexArray' is not a valid constraint.

But if TIndexArray is a class and not an array type it works.

You don't really need TType in your class declaration. You can just use TIndexArray<TArrayType> directly in your class, or declare TType = TIndexArray<TArrayType> within the class. — Dalija Prasnikar
– Dalija Prasnikar ♦, Commented Dec 22, 2022 at 10:17

Remy Lebeau · Accepted Answer · 2022-12-22 03:47:35Z

3

Array types are not supported as constraints. This is documented behavior:

Constraint items include:

Zero, one, or multiple interface types

Zero or one class type

The reserved word "constructor", "class", or "record"

No mention of array types.

answered Dec 22, 2022 at 3:47

Remy Lebeau

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