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Interpolation

Stylus supports interpolation by using the {} characters to surround an expression, which then becomes part of the identifier. For example, -webkit-{'border' + '-radius'} evaluates to -webkit-border-radius.

A great example use-case for this is expanding properties with vendor prefixes.

vendor(prop, args)
  -webkit-{prop} args
  -moz-{prop} args
  {prop} args

border-radius()
  vendor('border-radius', arguments)

box-shadow()
  vendor('box-shadow', arguments)

button
  border-radius 1px 2px / 3px 4px
vendor(prop, args)
  -webkit-{prop} args
  -moz-{prop} args
  {prop} args

border-radius()
  vendor('border-radius', arguments)

box-shadow()
  vendor('box-shadow', arguments)

button
  border-radius 1px 2px / 3px 4px

Yields:

button {
  -webkit-border-radius: 1px 2px / 3px 4px;
  -moz-border-radius: 1px 2px / 3px 4px;
  border-radius: 1px 2px / 3px 4px;
}
button {
  -webkit-border-radius: 1px 2px / 3px 4px;
  -moz-border-radius: 1px 2px / 3px 4px;
  border-radius: 1px 2px / 3px 4px;
}

Selector Interpolation

Interpolation works with selectors as well. For example, we may iterate to assign the height property for the first 5 rows in a table, as shown below:

table
  for row in 1 2 3 4 5
    tr:nth-child({row})
      height: 10px * row
table
  for row in 1 2 3 4 5
    tr:nth-child({row})
      height: 10px * row

Yields:

table tr:nth-child(1) {
  height: 10px;
}
table tr:nth-child(2) {
  height: 20px;
}
table tr:nth-child(3) {
  height: 30px;
}
table tr:nth-child(4) {
  height: 40px;
}
table tr:nth-child(5) {
  height: 50px;
}
table tr:nth-child(1) {
  height: 10px;
}
table tr:nth-child(2) {
  height: 20px;
}
table tr:nth-child(3) {
  height: 30px;
}
table tr:nth-child(4) {
  height: 40px;
}
table tr:nth-child(5) {
  height: 50px;
}

You may also put together multiple selectors into one variable by building a string and interpolate them in place:

mySelectors = '#foo,#bar,.baz'

{mySelectors}
  background: #000
mySelectors = '#foo,#bar,.baz'

{mySelectors}
  background: #000

Yields:

#foo,
#bar,
.baz {
  background: #000;
}
#foo,
#bar,
.baz {
  background: #000;
}