85 lines
2.2 KiB
Markdown
85 lines
2.2 KiB
Markdown
For Loop
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========
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{{#include ../links.md}}
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Iterating through a numeric [range] or an [array], or any type with a registered [type iterator],
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is provided by the `for` ... `in` loop.
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There are two alternative syntaxes, one including a counter variable:
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> `for` _variable_ `in` _expression_ `{` ... `}`
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>
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> `for (` _variable_ `,` _counter_ `)` `in` _expression_ `{` ... `}`
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~~~admonish tip.small "Tip: Disable `for` loops"
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`for` loops can be disabled via [`Engine::set_allow_looping`][options].
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~~~
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Break or Continue
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-----------------
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Like C, `continue` can be used to skip to the next iteration, by-passing all following statements.
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`break` can be used to break out of the loop unconditionally.
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For Expression
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--------------
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Unlike Rust, `for` statements can also be used as _expressions_.
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The `break` statement takes an optional expression that provides the return value.
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The default return value of a `for` expression is [`()`].
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~~~admonish tip.small "Tip: Disable all loop expressions"
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Loop expressions can be disabled via [`Engine::set_allow_loop_expressions`][options].
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~~~
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```js
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let a = [42, 123, 999, 0, true, "hello", "world!", 987.6543];
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// 'for' can be used just like an expression
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let index = for (item, count) in a {
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// if the 'for' loop breaks here, return a specific value
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switch item.type_of() {
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"i64" if item.is_even => break count,
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"f64" if item.to_int().is_even => break count,
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}
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// ... if the 'for' loop exits here, the return value is ()
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};
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if index == () {
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print("Magic number not found!");
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} else {
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print(`Magic number found at index ${index}!`);
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}
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```
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Counter Variable
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----------------
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The counter variable, if specified, starts from zero, incrementing upwards.
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```js , no_run
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let a = [42, 123, 999, 0, true, "hello", "world!", 987.6543];
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// Loop through the array
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for (item, count) in a {
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if x.type_of() == "string" {
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continue; // skip to the next iteration
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}
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// 'item' contains a copy of each element during each iteration
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// 'count' increments (starting from zero) for each iteration
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print(`Item #${count + 1} = ${item}`);
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if x == 42 { break; } // break out of for loop
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}
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```
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