Hi,

i have a function like this:
```
import std.algorithm.iteration : substitute;
//...
string replace(string content, string[] searches , string replace) {
	
	if(searches.empty) return content;

	auto result = content.substitute(searches.front,replace);
	for(size_t i=1; i < searches.length; i++) {
		searches.popFront();
		result = result.substitute(searches.front,replace);
	}
        //...
        return "example return";
}
```
I do not understand why this is not valid. This is the compilation Error:
```
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/iteration.d(5954,48): Error: template std.algorithm.searching.find cannot deduce function from argument types !(__lambda196)(Result, string), candidates are:
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/searching.d(1557,12):        find(alias pred = "a == b", InputRange, Element)(InputRange haystack, scope Element needle)
  with pred = __lambda196,
       InputRange = Result,
       Element = string
  must satisfy the following constraint:
       is(typeof(binaryFun!pred(haystack.front, needle)) : bool)
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/searching.d(1823,12):        find(alias pred, InputRange)(InputRange haystack)
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/searching.d(1877,4):        find(alias pred = "a == b", R1, R2)(R1 haystack, scope R2 needle)
  with pred = __lambda196,
       R1 = Result,
       R2 = string
  must satisfy the following constraint:
       isForwardRange!R1
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/searching.d(2329,23):        find(alias pred = "a == b", Range, Ranges...)(Range haystack, Ranges needles)
  with pred = __lambda196,
       Range = Result,
       Ranges = (string)
  must satisfy the following constraint:
       Ranges.length > 1
/home/mab/dlang/dmd-2.089.1/linux/bin64/../../src/phobos/std/algorithm/searching.d(2444,19):        find(RandomAccessRange, alias pred, InputRange)(RandomAccessRange haystack, scope BoyerMooreFinder!(pred, InputRange) needle)
source/app.d(44,29): Error: template instance std.algorithm.iteration.substitute!((a, b) => a == b, Result, string, string) error instantiating
source/app.d(44,29): Error: cannot implicitly convert expression substitute(result, front(searches), replace) of type std.algorithm.iteration.joiner!(MapResult!(__lambda7, SubstituteSplitter)).joiner.Result to std.algorithm.iteration.joiner!(MapResult!(__lambda7, SubstituteSplitter)).joiner.Result
/home/mab/dlang/dmd-2.089.1/linux/bin64/dmd failed with exit code 1.
```

Can someone explain what is going on? Specially this part: "Error: cannot implicitly convert expression substitute(result, front(searches), replace) of type std.algorithm.iteration.joiner!(MapResult!(__lambda7, SubstituteSplitter)).joiner.Result to std.algorithm.iteration.joiner!(MapResult!(__lambda7, SubstituteSplitter)).joiner.Result"

In the Example "Multiple substitutes" in https://dlang.org/phobos/std_algorithm_iteration.html#.substitute.substitute i understand that a call to substitute() can be made on the result of substitute().

Thanks

BTW: can sourcecode be formated in this forum somehow?

On Saturday, 11 January 2020 at 17:10:02 UTC, Martin Brezl wrote:
> Hi,
>
> i have a function like this:
> ```
>[...]
> auto result = content.substitute(searches.front,replace);
>	for(size_t i=1; i < searches.length; i++) {
>		searches.popFront();
>		result = result.substitute(searches.front,replace);
>       }
> [...]

`result = result.to!string.substitute(searches.front,replace);`

Convertring result to string solves the problem - but i do not understand why the Example "Multiple substitutes" from the docs is working.

On Saturday, 11 January 2020 at 17:10:02 UTC, Martin Brezl wrote:
> Hi,
>
> i have a function like this:
> ```
> import std.algorithm.iteration : substitute;
> //...
> string replace(string content, string[] searches , string replace) {
> 	
> 	if(searches.empty) return content;
>
> 	auto result = content.substitute(searches.front,replace);
> 	for(size_t i=1; i < searches.length; i++) {
> 		searches.popFront();
> 		result = result.substitute(searches.front,replace);
> 	}
>         //...
>         return "example return";
> }
> ```

The issue is the double assigned result.

auto result = content.substitute(searches.front,replace);
result = result.substitute(searches.front,replace);

`substitute` is going to return a template range typed off `content` then it uses that type to perform another substitution.

`content` and `result` don't have the same type.

You can also turn your function into a fold.

auto searches = ["1", "2"];
writeln (searches.fold!((a, b)  => a.substitute(b, "number").to!string)("come 1 come 2")) ;