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Changes between Initial Version and Version 1 of CoalesceOperator

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Timestamp:
12/20/10 00:46:52 (7 years ago)
Author:
todd.a
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  • CoalesceOperator

    v1 v1  
     1The '''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 
     8The expression evaluates to a unless that value is '''nil''', in which case, it evaluates to '''b'''. 
     9 
     10Although 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 
     12The 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 
     19In 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  
     24print name ? 'NONAME'  
     25 
     26# Example 2  
     27def foo(factor as decimal?)  
     28    factor ?= 1 # 'normalize' factor before proceeding with the rest of implementation  
     29    ... 
     30 
     31# Example 3  
     32get name as String 
     33    return _name ? .getType.name  
     34 
     35# Example 4  
     36# this:  
     37name = if(employee.manager.name<>nil, employee.manager.name, 'NONAME')  
     38# can evaluate the key expression twice and is less succinct than:  
     39name = employee.manager.name ? 'NONAME'  
     40}}}