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Add docs for closures.

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This commit is contained in:
Stephen Chung
2020-08-04 16:27:55 +08:00
parent 3d6c83c6d8
commit 4878a69503
13 changed files with 200 additions and 64 deletions
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13
doc/src/language/fn-capture.md
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@@ -16,6 +16,8 @@ it raises an evaluation error.
It is possible, through a special syntax, to capture the calling scope - i.e. the scope
that makes the function call - and access variables defined there.
Capturing can be disabled via the [`no_closure`] feature.
```rust
fn foo(y) { // function accesses 'x' and 'y', but 'x' is not defined
x += y; // 'x' is modified in this function
@@ -47,7 +49,7 @@ f.call!(41); // <- syntax error: capturing is not allowed in method-c
No Mutations
------------
Variables in the calling scope are accessed as copies.
Variables in the calling scope are captured as copies.
Changes to them do not reflect back to the calling scope.
Rhai functions remain _pure_ in the sense that they can never mutate their environment.
@@ -56,7 +58,10 @@ Rhai functions remain _pure_ in the sense that they can never mutate their envir
Caveat Emptor
-------------
Functions relying on the calling scope is a _Very Bad Idea™_ because it makes code almost impossible
to reason and maintain, as their behaviors are volatile and unpredictable.
Functions relying on the calling scope is often a _Very Bad Idea™_ because it makes code
almost impossible to reason and maintain, as their behaviors are volatile and unpredictable.
This usage should be at the last resort.
They behave more like macros that are expanded inline than actual function calls, thus the
syntax is also similar to Rust's macro invocations.
This usage should be at the last resort. YOU HAVE BEEN WARNED.