I faced this issue while working with custom formatting for a
struct. I have reduced the error down to this test program:
import std.format, std.stdio, std.array;
struct Test1
{
void toString(W, C)(ref W w, scope const ref FormatSpec!C fmt)
{
pragma(msg, "Test1 function compiled with W=" ~
W.stringof);
// formatValue(w, this, fmt);
}
}
struct Test2
{
void toString(W, C)(ref W w, scope const ref FormatSpec!C fmt)
{
pragma(msg, "Test2 function compiled with W=" ~
W.stringof);
formatValue(w, this, fmt);
}
}
void main()
{
Test1 t1;
Test2 t2;
Appender!string writer;
auto ff = singleSpec("%s");
formatValue(writer, t1, ff);
formatValue(writer, t2, ff);
}
When compiled, the output is:
Test1 function compiled with W=S
Test1 function compiled with W=Appender!string
Test2 function compiled with W=S
1. Why was Test2 never compiled with W=Appender!string?
2. What is "S"?
Essentially, my custom struct was not being formatted using the
toString method that I had written. Reducing the issue, it seems
like a call to formatValue with the same type caused the issue.
If someone can explain what I am doing wrong here, it would
really help a lot.
Thanks,
Saurabh