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128 lines
3.3 KiB
Plaintext
128 lines
3.3 KiB
Plaintext
---
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title: "@if and @else"
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table_of_contents: true
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introduction: >
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The `@if` rule is written `@if <expression> { ... }`, and it controls whether
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or not its block gets evaluated (including emitting any styles as CSS). The
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[expression](../../syntax/structure#expressions) usually returns either
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[`true` or `false`](../../values/booleans)—if the expression returns `true`,
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the block is evaluated, and if the expression returns `false` it’s not.
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---
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<%= partial 'code-snippets/example-if' %>
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## `@else`
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An `@if` rule can optionally be followed by an `@else` rule, written
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`@else { ... }`. This rule's block is evaluated if the `@if` expression returns
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`false`.
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<% example do %>
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$light-background: #f2ece4;
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$light-text: #036;
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$dark-background: #6b717f;
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$dark-text: #d2e1dd;
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@mixin theme-colors($light-theme: true) {
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@if $light-theme {
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background-color: $light-background;
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color: $light-text;
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} @else {
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background-color: $dark-background;
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color: $dark-text;
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}
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}
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.banner {
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@include theme-colors($light-theme: true);
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body.dark & {
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@include theme-colors($light-theme: false);
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}
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}
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===
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$light-background: #f2ece4
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$light-text: #036
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$dark-background: #6b717f
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$dark-text: #d2e1dd
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@mixin theme-colors($light-theme: true)
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@if $light-theme
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background-color: $light-background
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color: $light-text
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@else
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background-color: $dark-background
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color: $dark-text
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.banner
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@include theme-colors($light-theme: true)
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body.dark &
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@include theme-colors($light-theme: false)
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<% end %>
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### `@else if`
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You can also choose whether to evaluate an `@else` rule's block by writing it
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`@else if <expression> { ... }`. If you do, the block is evaluated only if the
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preceding `@if`'s expression returns `false` *and* the `@else if`'s expression
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returns `true`.
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In fact, you can to chain as many `@else if`s as you want after an `@if`. The
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first block in the chain whose expression returns `true` will be evaluated, and
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no others. If there's a plain `@else` at the end of the chain, its block will be
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evaluated if every other block fails.
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<% example do %>
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@mixin triangle($size, $color, $direction) {
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height: 0;
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width: 0;
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border-color: transparent;
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border-style: solid;
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border-width: $size / 2;
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@if $direction == up {
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border-bottom-color: $color;
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} @else if $direction == right {
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border-left-color: $color;
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} @else if $direction == down {
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border-top-color: $color;
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} @else if $direction == left {
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border-right-color: $color;
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} @else {
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@error "Unknown direction #{$direction}.";
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}
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}
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.next {
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@include triangle(5px, black, right);
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}
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===
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@mixin triangle($size, $color, $direction)
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height: 0
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width: 0
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border-color: transparent
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border-style: solid
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border-width: $size / 2
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@if $direction == up
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border-bottom-color: $color
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@else if $direction == right
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border-left-color: $color
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@else if $direction == down
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border-top-color: $color
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@else if $direction == left
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border-right-color: $color
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@else
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@error "Unknown direction #{$direction}."
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.next
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@include triangle(5px, black, right)
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<% end %>
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<%= partial 'documentation/snippets/truthiness-and-falsiness' %>
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