diff --git a/doc/src/language/fn-closure.md b/doc/src/language/fn-closure.md index b620e503..56c79cfd 100644 --- a/doc/src/language/fn-closure.md +++ b/doc/src/language/fn-closure.md @@ -49,7 +49,7 @@ f.call(2) == 42; // the value of 'x' is 40 because 'x' is sha // The above de-sugars into this: fn anon$1001(x, y) { x + y } // parameter 'x' is inserted -make_shared(x); // convert variable 'x' into a shared value +$make_shared(x); // convert variable 'x' into a shared value let f = Fn("anon$1001").curry(x); // shared 'x' is curried @@ -57,6 +57,24 @@ f.call(2) == 42; ``` +Constants are Not Captured +-------------------------- + +Constants are never shared. Their values are simply cloned. + +```rust +const x = 42; // constant variable 'x' + +let f = |y| x += y; // constant 'x' is cloned and not captured + +x.is_shared() == false; // 'x' is not shared + +f.call(10); // the cloned copy of 'x' is changed + +x == 42; // 'x' is not changed +``` + + Beware: Captured Variables are Truly Shared ------------------------------------------ @@ -64,7 +82,7 @@ The example below is a typical tutorial sample for many languages to illustrate that may accompany capturing external scope variables in closures. It prints `9`, `9`, `9`, ... `9`, `9`, not `0`, `1`, `2`, ... `8`, `9`, because there is -ever only one captured variable, and all ten closures capture the _same_ variable. +ever only _one_ captured variable, and all ten closures capture the _same_ variable. ```rust let funcs = []; @@ -78,7 +96,7 @@ funcs.len() == 10; // 10 closures stored in the array funcs[0].type_of() == "Fn"; // make sure these are closures for f in funcs { - f.call(); // all the references to 'i' are the same variable! + f.call(); // all references to 'i' are the same variable! } ```