On Monday, 11 October 2021 at 00:37:43 UTC, Paul Backus wrote:
On Monday, 11 October 2021 at 00:19:44 UTC, apz28 wrote:
/* Getting this error
onlineapp.d(34): Error: none of the overloads of `toString`
are callable using argument types `(Buffer)`, candidates are:
onlineapp.d(19): `onlineapp.Foo.toString()`
onlineapp.d(26): `onlineapp.Foo.toString(const(char)[]
fmt)`
onlineapp.d(22): `toString(Writer, Char)(return ref
Writer sink)`
*/
The signature of your `toString` method should match one of the
examples in [the documentation][1]:
```d
void toString(Writer, Char)(ref Writer w, const ref
FormatSpec!Char fmt)
void toString(Writer)(ref Writer w)
string toString();
```
Here is an example that works:
```d
import std.range: put;
import std.array: appender;
import std.format: formattedWrite;
struct Foo
{
void toString(Writer)(ref Writer writer)
{
put(writer, "Foo");
}
}
void main()
{
auto buffer = appender!string;
Foo foo;
formattedWrite(buffer, "%s", foo);
assert(buffer[] == "Foo");
}
```
Link: https://run.dlang.io/is/dZLRuo
[1]: https://phobos.dpldocs.info/std.format.write.html
On Monday, 11 October 2021 at 00:37:43 UTC, Paul Backus wrote:
The subject is why the call is not allowed (format is not mention
in question). Below sample is a bit more clear
import std.range.primitives : isOutputRange;
import std.traits: isSomeChar;
@safe:
struct Buffer(Char)
{
@safe:
void put(Char c)
{}
void put(scope const(Char)[] s)
{}
}
struct Foo
{
@safe:
ref Writer outWork(Writer)(return ref Writer sink)
if (isOutputRange!(Writer, char))
{return sink;}
// Remove " && isSomeChar!Char" does not make any
difference
ref Writer outFail(Writer, Char)(return ref Writer sink)
if (isOutputRange!(Writer, Char) && isSomeChar!Char)
{return sink;}
}
void main()
{
pragma(msg, isOutputRange!(Buffer!char, char)); // Print
true
Buffer!char buffer;
Foo foo;
foo.outWork(buffer); // OK
foo.outFail!(Buffer!char, char)(buffer); // OK with
explicit
foo.outFail(buffer); // NOT OK
}
/* Blow is output from online compiler
true
onlineapp.d(40): Error: template `onlineapp.Foo.outFail` cannot
deduce function from argument types `!()(Buffer!char)`,
candidates are:
onlineapp.d(25): `outFail(Writer, Char)(return ref Writer
sink)`
*/
