The adding of copy construtors to `Service`

defined as

```
@safe struct Service {
this(ref return scope typeof(this) rhs) {}
this(const ref return scope typeof(this) rhs) const {}
}
@safe struct Session {
void openAndGetService(in string key) scope {
import std.algorithm.searching : find;
auto hit = _pairs.find!((x) => x.key == key)();
}
private Pair[] _pairs;
private struct Pair {
string key;
Service service;
}
}
```

makes a call to find error as

```
copy_ctor_find_fail.d(9): Error: template `std.algorithm.searching.find` cannot deduce function from argument types `!((x) => x.key == key)(Pair[])`, candidates are:
auto hit = _pairs.find!((x) => x.key == key)();
^
std/algorithm/searching.d(1559): `find(alias pred = "a == b", InputRange, Element)(InputRange haystack, scope Element needle)`
InputRange find(alias pred = "a == b", InputRange, Element)(InputRange haystack, scope Element needle)
^
std/algorithm/searching.d(1827): `find(alias pred, InputRange)(InputRange haystack)`
with `pred = __lambda2,
InputRange = Pair[]`
must satisfy the following constraint:
` isInputRange!InputRange`
InputRange find(alias pred, InputRange)(InputRange haystack)
^
std/algorithm/searching.d(1881): `find(alias pred = "a == b", R1, R2)(R1 haystack, scope R2 needle)`
R1 find(alias pred = "a == b", R1, R2)(R1 haystack, scope R2 needle)
^
std/algorithm/searching.d(2340): `find(alias pred = "a == b", Range, Ranges...)(Range haystack, Ranges needles)`
with `pred = __lambda2,
Range = Pair[],
Ranges = ()`
must satisfy the following constraint:
` Ranges.length > 1`
Tuple!(Range, size_t) find(alias pred = "a == b", Range, Ranges...)
^
std/algorithm/searching.d(2455): `find(RandomAccessRange, alias pred, InputRange)(RandomAccessRange haystack, scope BoyerMooreFinder!(pred, InputRange) needle)`
RandomAccessRange find(RandomAccessRange, alias pred, InputRange)(
^```
Using
```d
auto hit = _pairs.find!((scope const ref x) => x.key == key)();
```

fails in the same way. What's wrong?