https://issues.dlang.org/show_bug.cgi?id=23643
Issue ID: 23643
Summary: [betterC] Better Error Message For CTFE GC Usage
Product: D
Version: D2
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P1
Component: dmd
Assignee: [email protected]
Reporter: [email protected]
Consider the following real code example,
char[] unsignedToTempString(uint radix = 10)(ulong value, return scope
char[] buf) @safe
if (radix >= 2 && radix <= 16)
{
size_t i = buf.length;
do
{
uint x = void;
if (value < radix)
{
x = cast(uint)value;
value = 0;
}
else
{
x = cast(uint)(value % radix);
value /= radix;
}
buf[--i] = cast(char)((radix <= 10 || x < 10) ? x + '0' : x - 10 +
'a');
} while (value);
return buf[i .. $];
}
char[] myToString(ulong n)
{
char[20] buf;
auto s = unsignedToTempString(n, buf);
return s ~ (n > uint.max ? "UL" : "U");
}
enum a = myToString(5);
This gives the following error
Error: array concatenation of expression `cast(const(char)[])s ~ (n >
4294967295LU ? "UL" : "U")` requires the GC which is not available with
-betterC
The problem here is that DMD is trying to include the function myToString into
the object file even though it's only being used during CTFE. The fix for this
code is to make myToString a template. But the chance that a user is going to
know that is very low.
The compiler knows that it encountered this function during the CTFE run. So it
should give a helpful error message, something like.
Error: array concatenation of expression `cast(const(char)[])s ~ (n >
4294967295LU ? "UL" : "U")` requires the GC which is not available with
-betterC
This GC allocation was encountered during CTFE. If this function is
supposed to be a CTFE only function then this error can be fixed by making the
function a template.
Simple, easy to understand, and very helpful.
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