Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.14)
// Compass (v1.0.3)
// ----

/* Solution 1 */
$_selectors: '';
@for $i from 1 through 12 {
  $_selectors: '#{$_selectors}.truc_#{$i}';
}
#{simple-selectors($_selectors)} {
  property: value;
}

/* Solution 2 */
%truc {
  property: value;
}
@for $i from 1 through 12 {
  .truc_#{$i} {
    @extend %truc; 
  }
}

SassMeister-output.css

/* Solution 1 */
.truc_1, .truc_2, .truc_3, .truc_4, .truc_5, .truc_6, .truc_7, .truc_8, .truc_9, .truc_10, .truc_11, .truc_12 {
  property: value;
}

/* Solution 2 */
.truc_1, .truc_2, .truc_3, .truc_4, .truc_5, .truc_6, .truc_7, .truc_8, .truc_9, .truc_10, .truc_11, .truc_12 {
  property: value;
}