Open Array vs Dyn Array as argument type in functions, changes in FPC
3.3
lazarus / 62-General

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prof7bit · 2021-09-23 10:07

Consider this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1; type  TBytes = array of Byte; procedure Foo(A: array of
Byte);beginend; procedure Bar(A: TBytes);beginend; var  X:
array[0..15] of Byte; begin  Foo(X);  Bar(X); // error in FPC 3.3.1,
compiles fine in 3.2.1end. 
The above code has been compiling and working fine in FPC 3.2 but it
fails to compile in FPC main. The error is:

Incompatible type for arg no. 1: Got "Array[0..15] Of Byte", expected
"TBytes"

Is this intentional? Was the previous behavior a bug? I can vaguely
remember being mildly surprised when I found out that I can use it
like in the code above, but then did not spend any more thoughts on
it.

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marcov · 2021-09-23 10:20

I don't know, but if you look at the 3.2.x assembler, it effectively
seems to create a TBytes temp, and this is indeed not very nice:

Code: [Select]  leal    -4(%ebp),%eax
        movl    $RTTI_$P$PROJECT1_$$_TBYTES,%edx
        call    fpc_dynarray_clear
        movl    $16,-8(%ebp)
        leal    -8(%ebp),%eax
        pushl   %eax
        movl    $RTTI_$P$PROJECT1_$$_TBYTES,%edx
        movl    $1,%ecx
        leal    -4(%ebp),%eax
        call    fpc_dynarray_setlength
        movl    -4(%ebp),%edi
        movl    $U_$P$PROJECT1_$$_X,%esi
        movl    $4,%ecx
        rep
        movsl
        movl    -4(%ebp),%eax
        call    P$PROJECT1_$$_BAR$TBYTES

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PascalDragon · 2021-09-23 11:28

Quote from: prof7bit on September 23, 2021, 12:07:33 pmThe above code
has been compiling and working fine in FPC 3.2 but it fails to compile
in FPC main. The error is:

Incompatible type for arg no. 1: Got "Array[0..15] Of Byte", expected
"TBytes"

Is this intentional? Was the previous behavior a bug? I can vaguely
remember being mildly surprised when I found out that I can use it
like in the code above, but then did not spend any more thoughts on
it.

Yes, this is intentional and documented.