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On Friday, 5 April 2024 at 14:41:12 UTC, Carl Sturtivant wrote:
>On Friday, 5 April 2024 at 07:37:20 UTC, Paolo Invernizzi wrote:
>pragma(msg, x) ?
No.
__ctfeWrite(x) is executed inside an executing function like any other statement in it, and can have an argument x computed during that execution.
It is defined to output the computed text x to stderr when the function it is a part of is called as CTFE by the compiler and to be a no-op if that function is called at run time in the compiled executable.
So it is a replacement for std.stdio.write in a CTFE function, handy among other things for reporting what's going on during the execution of that function by the compiler.
pragma(msg, x) works during its compilation, so putting it as a line in a CTFE-called function would not execute it when the function is called by the compiler. That being the case, x may not be a value computed when that function executes. Such a value is "not available at compile time", only at CTFE run time. The CTFE function is not running when it is being compiled.
It is possible that x in pragma(msg, x) be computed with a call to a function as its return value, i.e. computed by CTFE, but that call will be made when pragma(msg, x) is compiled, and is a part of compiling it. Only when the function has returned producing x does the pragma(msg, x) do its work.
This works:
alias E = double;
auto r = 0.iota!E(1,.05)
static this()
{
alias ranges = imported!"std.meta".AliasSeq!(isRandomAccessRange,
isForwardRange, isInputRange, isOutputRange, isBidirectionalRange);
static foreach(R; ranges) pragma(msg, R!(typeof(r), E));
}
void main() {}
SDB@79