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Template `std.typecons.borrow`

Borrows the payload of SafeRefCounted for use in fun. Inferred as @safe if fun is @safe and does not escape a reference to the payload. The reference count will be incremented for the duration of the operation, so destroying the last reference will not leave dangling references in fun.



template borrow(alias fun)
;

Contained Functions

Name	Description
borrow

Parameters

Name	Description
fun	A callable accepting the payload either by value or by reference.
refCount	The counted reference to the payload.

Returns

The return value of fun, if any. ref in the return value will be forwarded.

Issues

For yet unknown reason, code that uses this function with UFCS syntax will not be inferred as @safe. It will still compile if the code is explicitly marked @safe and nothing in fun prevents that.

Example

This example can be marked @safe with -preview=dip1000.

auto rcInt = safeRefCounted(5);
writeln(rcInt.borrow!(theInt => theInt)); // 5
auto sameInt = rcInt;
writeln(sameInt.borrow!"a"); // 5

// using `ref` in the function
auto arr = [0, 1, 2, 3, 4, 5, 6];
sameInt.borrow!(ref (x) => arr[x]) = 10;
writeln(arr); // [0, 1, 2, 3, 4, 10, 6]

// modifying the payload via an alias
sameInt.borrow!"a*=2";
writeln(rcInt.borrow!"a"); // 10

Authors

Andrei Alexandrescu, Bartosz Milewski, Don Clugston, Shin Fujishiro, Kenji Hara

License

Boost License 1.0.