64f4021c40
I decided to break if-let out, as it's too complex for this part, but moving if that late seems silly too.
74 lines
1.6 KiB
Markdown
74 lines
1.6 KiB
Markdown
% if
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Rust’s take on `if` is not particularly complex, but it’s much more like the
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`if` you’ll find in a dynamically typed language than in a more traditional
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systems language. So let’s talk about it, to make sure you grasp the nuances.
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`if` is a specific form of a more general concept, the ‘branch’. The name comes
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from a branch in a tree: a decision point, where depending on a choice,
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multiple paths can be taken.
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In the case of `if`, there is one choice that leads down two paths:
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```rust
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let x = 5;
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if x == 5 {
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println!("x is five!");
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}
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```
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If we changed the value of `x` to something else, this line would not print.
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More specifically, if the expression after the `if` evaluates to `true`, then
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the block is executed. If it’s `false`, then it is not.
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If you want something to happen in the `false` case, use an `else`:
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```rust
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let x = 5;
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if x == 5 {
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println!("x is five!");
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} else {
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println!("x is not five :(");
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}
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```
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If there is more than one case, use an `else if`:
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```rust
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let x = 5;
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if x == 5 {
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println!("x is five!");
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} else if x == 6 {
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println!("x is six!");
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} else {
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println!("x is not five or six :(");
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}
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```
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This is all pretty standard. However, you can also do this:
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```rust
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let x = 5;
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let y = if x == 5 {
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10
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} else {
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15
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}; // y: i32
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```
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Which we can (and probably should) write like this:
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```rust
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let x = 5;
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let y = if x == 5 { 10 } else { 15 }; // y: i32
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```
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This works because `if` is an expression. The value of the expression is the
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value of the last expression in whichever branch was chosen. An `if` without an
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`else` always results in `()` as the value.
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