Example from docs:
string s = "hello!124:34.5";
string a;
int b;
double c;
formattedRead(s, "%s!%s:%s", &a, &b, &c);
assert(a == "hello" && b == 124 && c == 34.5);

now changing the first formattedRead argument to a string literal:
formattedRead("hello!124:34.5", "%s!%s:%s", &a, &b, &c);

results in this compiler error:
Error: template std.format.formattedRead cannot deduce function from argument types !()(string, string, string*, int*, double*), candidates are:
..\..\src\phobos\std\format.d(588,6):
std.format.formattedRead(R, Char, S...)(ref R r, const(Char)[] fmt, S args)

I am not getting the point that in both cases the argument is a string, but in the first case it is interpreted as a Range, and in the second case not. Why?

On Thu, Mar 31, 2016 at 06:23:21PM +0000, ParticlePeter via Digitalmars-d-learn wrote:
> Example from docs:
> string s = "hello!124:34.5";
> string a;
> int b;
> double c;
> formattedRead(s, "%s!%s:%s", &a, &b, &c);
> assert(a == "hello" && b == 124 && c == 34.5);
> 
> now changing the first formattedRead argument to a string literal: formattedRead("hello!124:34.5", "%s!%s:%s", &a, &b, &c);
> 
> results in this compiler error:
> Error: template std.format.formattedRead cannot deduce function from
> argument types !()(string, string, string*, int*, double*), candidates are:
> ..\..\src\phobos\std\format.d(588,6):
> std.format.formattedRead(R, Char, S...)(ref R r, const(Char)[] fmt, S args)
> 
> I am not getting the point that in both cases the argument is a
> string, but in the first case it is interpreted as a Range, and in the
> second case not.
> Why?

Because in the second case the string is an rvalue, whereas in the first case it gets stored in a variable first, so it's an lvalue.  The first parameter of formattedRead is 'ref', meaning that it requires an lvalue.

(Arguably, it should be `auto ref` instead, then literals would work, but that belongs in an enhancement request.)


T

-- 
Государство делает вид, что платит нам зарплату, а мы делаем вид, что работаем.

On Thursday, 31 March 2016 at 18:25:45 UTC, H. S. Teoh wrote:
> On Thu, Mar 31, 2016 at 06:23:21PM +0000, ParticlePeter via Digitalmars-d-learn wrote:
>> Example from docs:
>> string s = "hello!124:34.5";
>> string a;
>> int b;
>> double c;
>> formattedRead(s, "%s!%s:%s", &a, &b, &c);
>> assert(a == "hello" && b == 124 && c == 34.5);
>> 
>> now changing the first formattedRead argument to a string literal: formattedRead("hello!124:34.5", "%s!%s:%s", &a, &b, &c);
>> 
>> results in this compiler error:
>> Error: template std.format.formattedRead cannot deduce function from
>> argument types !()(string, string, string*, int*, double*), candidates are:
>> ..\..\src\phobos\std\format.d(588,6):
>> std.format.formattedRead(R, Char, S...)(ref R r, const(Char)[] fmt, S args)
>> 
>> I am not getting the point that in both cases the argument is a
>> string, but in the first case it is interpreted as a Range, and in the
>> second case not.
>> Why?
>
> Because in the second case the string is an rvalue, whereas in the first case it gets stored in a variable first, so it's an lvalue.  The first parameter of formattedRead is 'ref', meaning that it requires an lvalue.
>
> (Arguably, it should be `auto ref` instead, then literals would work, but that belongs in an enhancement request.)
>
>
> T

Ok, thanks, that makes sense. I would add that the compiler should mention that a ref value is required, this would have helped to understand the issue.