| | 1 | The '''coalesce''' binary expression evaluates to the first non-nil value. There is an augmented assignment version of it as well. |
| | 2 | |
| | 3 | === Grammar === |
| | 4 | {{{ |
| | 5 | <a> ? <b> |
| | 6 | }}} |
| | 7 | |
| | 8 | The expression evaluates to a unless that value is '''nil''', in which case, it evaluates to '''b'''. |
| | 9 | |
| | 10 | Although uncommon, nothing prevents b itself from also being '''nil'''. Neither expression will be evaluated more than once and if a is non-nil then b will not be evaluated at all. |
| | 11 | |
| | 12 | The type of the coalesce expression is the greatest common denominator between the type of '''a''' and the type of '''b'''. |
| | 13 | |
| | 14 | === Grammar === |
| | 15 | {{{ |
| | 16 | <a> ?= <b> |
| | 17 | }}} |
| | 18 | |
| | 19 | In the augmented assignment version, the result is assigned back to a. This requires that b is type compatible with a or a compilation error will occur. |
| | 20 | |
| | 21 | {{{ |
| | 22 | #!cobra |
| | 23 | # Example 1 |
| | 24 | print name ? 'NONAME' |
| | 25 | |
| | 26 | # Example 2 |
| | 27 | def foo(factor as decimal?) |
| | 28 | factor ?= 1 # 'normalize' factor before proceeding with the rest of implementation |
| | 29 | ... |
| | 30 | |
| | 31 | # Example 3 |
| | 32 | get name as String |
| | 33 | return _name ? .getType.name |
| | 34 | |
| | 35 | # Example 4 |
| | 36 | # this: |
| | 37 | name = if(employee.manager.name<>nil, employee.manager.name, 'NONAME') |
| | 38 | # can evaluate the key expression twice and is less succinct than: |
| | 39 | name = employee.manager.name ? 'NONAME' |
| | 40 | }}} |
