• Mark (13/13) Dec 06 2017 std.format has the function formattedRead which can be used to
• =?UTF-8?Q?Ali_=c3=87ehreli?= (8/14) Dec 06 2017 formattedRead takes the first parameter as 'ref'.
• Mark (4/21) Dec 06 2017 I see. That's somewhat inconvenient.
• Adam D. Ruppe (14/15) Dec 07 2017 You could write a little wrapper function to do that

Mark <smarksc gmail.com> writes:

std.format has the function formattedRead which can be used to 
parse a string, e.g.

string first_name;
string last_name;
string info = readln();
formattedRead(info, "%s %s", first_name, last_name);

This piece of code works as intended. However, since I don't need 
the input after it's parsed, I wanted to omit the 3rd line of 
code above and replace the 4th line with

formattedRead(readln(), "%s %s", first_name, last_name);

But this raises a compilation error, claiming that formattedRead 
"cannot deduce function from argument types". What's the problem 
here?

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 12/06/2017 10:47 AM, Mark wrote:

 string info = readln();
 formattedRead(info, "%s %s", first_name, last_name);

 This piece of code works

 formattedRead(readln(), "%s %s", first_name, last_name);

 But this raises a compilation error, claiming that formattedRead "cannot
 deduce function from argument types".

formattedRead takes the first parameter as 'ref'.

I hope we can change compiler error messages like this. What it means is 
that although the 'string' part of the argument matched, it cannot be 
passed as 'ref' because what readln() returns is an rvalue. (On the 
other hand, info above is an lvalue.) rvalues cannot be bound to 
references in D.

Ali

Mark <smarksc gmail.com> writes:

On Wednesday, 6 December 2017 at 18:57:55 UTC, Ali Çehreli wrote:
 On 12/06/2017 10:47 AM, Mark wrote:

 string info = readln();
 formattedRead(info, "%s %s", first_name, last_name);

 This piece of code works

 formattedRead(readln(), "%s %s", first_name, last_name);

 But this raises a compilation error, claiming that

 formattedRead "cannot
 deduce function from argument types".

 formattedRead takes the first parameter as 'ref'.

 I hope we can change compiler error messages like this. What it 
 means is that although the 'string' part of the argument 
 matched, it cannot be passed as 'ref' because what readln() 
 returns is an rvalue. (On the other hand, info above is an 
 lvalue.) rvalues cannot be bound to references in D.

 Ali


I see. That's somewhat inconvenient.

I recall there was some debate(s) about allowing rvalues as const 
references (like in C++). What was the verdict on that?

Adam D. Ruppe <destructionator gmail.com> writes:

On Wednesday, 6 December 2017 at 18:47:03 UTC, Mark wrote:
 formattedRead(readln(), "%s %s", first_name, last_name);

You could write a little wrapper function to do that

uint myformattedRead (R, Char, S...)(R r, const(Char)[] fmt, auto 
ref S args) {
     formattedRead(r, fmt, args);
}


It just strips the ref off of the input string but otherwise 
forwards the same thing.

The reason it is ref tho btw is that that allows it to continue 
off a particular input; you can do like

string s;
formattedRead(s, ....)
formattedRead(s, ....) // this one picks up where the last one 
left off