Why is that?

import std.stdio, std.array

void main() {
  auto output = appender!(string);
  output ~= "world!";
//  output.data.insertInPlace(0, "Hello, ");  // Doesn't work
  auto asString = output.data;
  asString.insertInPlace(0, "Hello, ");  // Works
  writeln(asString);  // prints "Hello, world!"
}

Error: template std.array.insertInPlace cannot deduce function from argument types !()(string, int, string), candidates are:
.dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1031):        std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (!isSomeString!(T[]) && allSatisfy!(isInputRangeOrConvertible!T, U) && U.length > 0)
.dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1097):        std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (isSomeString!(T[]) && allSatisfy!(isCharOrStringOrDcharRange, U))

On Monday, 22 September 2014 at 14:45:31 UTC, Chris wrote:
> Why is that?
>
> import std.stdio, std.array
>
> void main() {
>   auto output = appender!(string);
>   output ~= "world!";
> //  output.data.insertInPlace(0, "Hello, ");  // Doesn't work
>   auto asString = output.data;
>   asString.insertInPlace(0, "Hello, ");  // Works
>   writeln(asString);  // prints "Hello, world!"
> }
>
> Error: template std.array.insertInPlace cannot deduce function from argument types !()(string, int, string), candidates are:
> .dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1031):
>        std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (!isSomeString!(T[]) && allSatisfy!(isInputRangeOrConvertible!T, U) && U.length > 0)
> .dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1097):
>        std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (isSomeString!(T[]) && allSatisfy!(isCharOrStringOrDcharRange, U))

output.data is a method returning a string. That is, the returned
string is not an lvalue, it doesn't have an address, it cannot
be passed in a ref parameter. But insertInPlace's first parameter
is ref. So, no can do.

Also note that `writeln(output.data);` prints "world!" without
"Hello, ".

On Monday, 22 September 2014 at 15:00:09 UTC, anonymous wrote:
> On Monday, 22 September 2014 at 14:45:31 UTC, Chris wrote:
>> Why is that?
>>
>> import std.stdio, std.array
>>
>> void main() {
>>  auto output = appender!(string);
>>  output ~= "world!";
>> //  output.data.insertInPlace(0, "Hello, ");  // Doesn't work
>>  auto asString = output.data;
>>  asString.insertInPlace(0, "Hello, ");  // Works
>>  writeln(asString);  // prints "Hello, world!"
>> }
>>
>> Error: template std.array.insertInPlace cannot deduce function from argument types !()(string, int, string), candidates are:
>> .dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1031):
>>       std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (!isSomeString!(T[]) && allSatisfy!(isInputRangeOrConvertible!T, U) && U.length > 0)
>> .dvm/compilers/dmd-2.066.0/linux/bin/../../src/phobos/std/array.d(1097):
>>       std.array.insertInPlace(T, U...)(ref T[] array, size_t pos, U stuff) if (isSomeString!(T[]) && allSatisfy!(isCharOrStringOrDcharRange, U))
>
> output.data is a method returning a string. That is, the returned
> string is not an lvalue, it doesn't have an address, it cannot
> be passed in a ref parameter. But insertInPlace's first parameter
> is ref. So, no can do.

I see. Thanks.

> Also note that `writeln(output.data);` prints "world!" without
> "Hello, ".

Because I only append "world!" to it. You would have to print the
variable "asString" to get "Hello, world!"