Details
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Type:
New Feature
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Status:
Resolved
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Priority:
Minor
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Resolution: Fixed
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Affects Version/s: 0.8.1
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Fix Version/s: 0.8.2
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Component/s: None
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Labels:None
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Number of attachments :
Description
for <target_list> in <enumerable>: <for_block> else: <else_block>
<else_block> is only executed when the loop terminates because <enumerable>.MoveNext() returns false when evaluated, i.e. whenever the <enumerable> attempts to move to the next item, but the <enumerable> is exhausted. This also means that if <enumerable> has no item at the first 'iteration', <enumerable>.MoveNext() will return false, and the <else_block> will be executed.
while <expression>: <while_block> else: <else_block>
<else_block> is only executed when the loop terminates the <expression> is tested but resolves to a false, null, or 0 value. This also means that if <expression> is false the first time it is tested (even before entering <while_block>) <else_block> will be executed.
The effect is that for these loops, <else_block> will not be executed when execution leaves the loop due to a break, raise, or return because <expression>/<enumerable>.MoveNext() is not evaluated. Note that the cause of the <else-block> executing is the condition evaluating to false.
Issue Links
| This issue relates to: | ||||
| BOO-991 | Implement a loop feature that executes only if the loop condition fails on its first execution |
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| This issue is related to: | ||||
| BOO-995 | Add the "or" keyword semantic for for/while loops |
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| This issue is superceded by: | ||||
| BOO-996 | Modify the for/while "else" semantic to use a new keyword: "then" |
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This change should be minimally invasive, and as it adds to the language without adversely increasing complexity, I have no problems with it being implemented.