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Add constants.

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Stephen Chung
2020-03-13 18:12:41 +08:00
parent 9bd66c7db3
commit 9844ae8665
9 changed files with 426 additions and 155 deletions
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README.md
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@@ -57,8 +57,8 @@ Related
Other cool projects to check out:
* [ChaiScript] - A strong inspiration for Rhai. An embedded scripting language for C++ that I helped created many moons ago, now being lead by my cousin.
* You can also check out the list of [scripting languages for Rust] on [awesome-rust].
* [ChaiScript](http://chaiscript.com/) - A strong inspiration for Rhai. An embedded scripting language for C++ that I helped created many moons ago, now being lead by my cousin.
* You can also check out the list of [scripting languages for Rust](https://github.com/rust-unofficial/awesome-rust#scripting) on [awesome-rust](https://github.com/rust-unofficial/awesome-rust)
Examples
--------
@@ -597,6 +597,17 @@ Variables in Rhai follow normal naming rules (i.e. must contain only ASCII lette
let x = 3;
```
Constants
---------
Constants can be defined and are immutable. Constants follow the same naming rules as [variables](#variables).
```rust
const x = 42;
print(x * 2); // prints 84
x = 123; // <- syntax error - cannot assign to constant
```
Numbers
-------
@@ -1108,10 +1119,12 @@ The above script optimizes to:
}
```
Constant propagation is used to remove dead code:
Constants propagation is used to remove dead code:
```rust
if true || some_work() { print("done!"); } // since '||' short-circuits, 'some_work' is never called
const abc = true;
if abc || some_work() { print("done!"); } // 'abc' is constant so it is replaced by 'true'...
if true || some_work() { print("done!"); } // since '||' short-circuits, 'some_work' is never called because the LHS is 'true'
if true { print("done!"); } // <-- the line above is equivalent to this
print("done!"); // <-- the line above is further simplified to this
// because the condition is always true
@@ -1169,10 +1182,6 @@ engine.set_optimization(false); // turn off the optimizer
```
[ChaiScript]: http://chaiscript.com/
[scripting languages for Rust]: https://github.com/rust-unofficial/awesome-rust#scripting
[awesome-rust]: https://github.com/rust-unofficial/awesome-rust
[`num-traits`]: https://crates.io/crates/num-traits/
[`debug_msgs`]: #optional-features
[`unchecked`]: #optional-features