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.
