32-bit and 64-bit different type for Length of dynamic array?

Question

I have a DUnitX test suite running fine on Win32. But when I try to compile it for Win64, this line produces a compilation error:

Assert.AreEqual(4, Length(r.Values));

[dcc64 Error] ...: E2532 Couldn't infer generic type argument from different argument types for method 'AreEqual'

r.Values is defined as:

Type TIntegers = TArray<Integer>

Assert.AreEqual has different overloaded implementations and dcc64 can't choose the right one... ok, but why? And why can dcc32 compile this without a problem?

The only clue I have is that if I hover with the mouse, Delphi will tell me that Length is of type System.Smallint. There is no Assert.AreEqual implementation with Smallint parameters... and sure enough, if I cast it to Integer, dcc64 will compile it.

But this is bugging me a lot. If I look into the System.pas unit I can see that DynArraySetLength takes a NativeInt parameter... a 64 bit integer (I'd expect unsigned, but not sure about that). So why should Length return a 16 bit signed integer? That would seem like trouble waiting to happen, right?

What am I missing?

Answer 1

In 64 bit, TArray has a length of type Int64. As far as I can tell, there is no AreEqual overload for Int64, so it tries to use the generic version: AreEqual<>. But it looks as if, from the parameters, it can't decide which one.

So in Win64, do:

 Assert.AreEqual<Int64>(4, Length(r.Values));

or

 Assert.AreEqual(4, Integer(Length(r.Values)));

The latter is of course the easiest, as it should work in Win32 and Win64, but may not be able to cope with very huge arrays.

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FWIW, Length does not return a Smallint. But for functions that differ between platforms, especially "compiler magic" functions like Length, such (wrong) information can happen. That is a problem with the IDE, not with the compiler.

Update:

It may be easier, as @RemyLebeau said, to use NativeInt instead. That should work for both Win32 and Win64, as NativeInt is Int32 in Win32 and Int64 in Win64, and it is also what _DynArrayLength returns:

Assert.AreEqual<NativeInt>(4, Length(r.Values));