| // Copyright 2017 The LUCI Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // Package sortby provides a succinct way to generate correctly-behaved Less |
| // functions for use with the stdlib 'sort' package. |
| package sortby |
| |
| // LessFn is the type of the function which compares element i with element j of |
| // a given slice. Unlike the stdlib sort interpretation of this function, |
| // a LessFn in sortby should only compare a single field in your datastructure's |
| // elements. Multiple LessFns can be composed with Chain to create a composite |
| // Less implementation to pass to sort. |
| type LessFn func(i, j int) bool |
| |
| // Chain is a list of LessFns, each of which sorts a single aspect of your |
| // object. Nil LessFns will be ignored. |
| type Chain []LessFn |
| |
| // Use is a sort-compatible LessFn that actually executes the full chain of |
| // comparisons. |
| func (c Chain) Use(i, j int) bool { |
| for _, less := range c { |
| if less == nil { |
| continue |
| } |
| if less(i, j) { |
| return true |
| } else if less(j, i) { |
| return false |
| } |
| } |
| return false |
| } |