On Thu, 23 Aug 2012 07:33:13 -0400, monarch_dodra <monarchdo...@gmail.com>
wrote:
As title implies:
----
import std.stdio;
import std.format;
void main()
{
string s = "42";
int v;
formattedRead(s, "%d", &v);
writefln("[%s] [%s]", s, v);
}
----
[] [42]
----
Is this the "expected" behavior?
Furthermore, it is not possible to try to "save" s:
----
import std.stdio;
import std.format;
import std.range;
void main()
{
string s = "42";
int v;
formattedRead(s.save, "%d", &v);
writefln("[%s] [%s]", s, v);
}
----
main.d(9): Error: template std.format.formattedRead does not match any
function template declaration
C:\D\dmd.2.060\dmd2\windows\bin\..\..\src\phobos\std\format.d(526):
Error: template std.format.formattedRead(R,Char,S...) cannot deduce
template function from argument types !()(string,string,int*)
----
The workaround is to have a named backup:
auto ss = s.save;
formattedRead(ss, "%d", &v);
I've traced the root issue to formattedRead's signature, which is:
uint formattedRead(R, Char, S...)(ref R r, const(Char)[] fmt, S args);
Is there a particular reason for this pass by ref? It is inconsistent
with the rest of phobos, or even C's scanf?
Is this a file-able bug_report/enhancement_request?
I believe it behaves as designed, but could be designed in such a way that
does not need ref input range. In fact, I think actually R needing to be
ref is a bad thing. Consider that if D didn't consider string literals to
be lvalues (an invalid assumption IMO), then passing a string literal as
the input would not work!
The only issue is, what if you *do* want ref behavior for strings? You
would need to wrap the string into a ref'd range. That is not a good
proposition. Unfortunately, the way IFTI works, there isn't an
opportunity to affect the parameter type IFTI decides to use.
I think a reasonable enhancement would be to add a formattedReadNoref (or
better named alternative) that does not take a ref argument.
-Steve
