Difference between revisions of "Once"
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(Created page with "==A definition of <TT>once</TT>== A <TT>once</TT> feature is implemented by replacing the '''do''' keyword by '''once''' e. g.: foo: INTEGER is once Result := 1 e…") |
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==A definition of <TT>once</TT>== |
==A definition of <TT>once</TT>== |
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| − | A <TT>once</TT> |
+ | A <TT>once</TT> function is implemented by replacing the '''do''' keyword by '''once''' e. g.: |
foo: INTEGER is |
foo: INTEGER is |
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once |
once |
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end |
end |
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| − | This has the effect, that code of the feature is only executed once in the system lifetime. If the feature is a function (i. e. has a return type) every call of the feature will return the same ''Result'', be it an expanded value or a reference. For references, the references object may change over time, but the once function will always return the identical object. |
+ | This has the effect, that code of the feature is only executed once in the system lifetime. If the feature is a function (i. e. has a return type) every call of the feature will return the same ''Result'', be it an expanded value or a reference. For references, the references object may change over time, but the once function will always return the identical object. The routines body is executed only once, even if it is called via different names. I. e.: |
| + | foo, bar: INTEGER is |
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| + | once |
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| + | count := count + 1 |
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| + | Result := count |
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| + | end |
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| + | |||
| + | make is |
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| + | do |
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| + | assert(foo = 1) |
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| + | assert(bar = 1) |
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| + | end |
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| + | |||
| + | count: INTEGER |
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==Further Aspects== |
==Further Aspects== |
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| + | * once is not applicable to attributes |
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* ''once "manifest string"'' |
* ''once "manifest string"'' |
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* once per object (other eiffel compilers have ''once ("OBJECT")'' to execute the feature body once per object) in Liberty there are no plans to implement such a feature |
* once per object (other eiffel compilers have ''once ("OBJECT")'' to execute the feature body once per object) in Liberty there are no plans to implement such a feature |
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Latest revision as of 12:27, 24 March 2013
A definition of once
A once function is implemented by replacing the do keyword by once e. g.:
foo: INTEGER is
once
Result := 1
end
This has the effect, that code of the feature is only executed once in the system lifetime. If the feature is a function (i. e. has a return type) every call of the feature will return the same Result, be it an expanded value or a reference. For references, the references object may change over time, but the once function will always return the identical object. The routines body is executed only once, even if it is called via different names. I. e.:
foo, bar: INTEGER is
once
count := count + 1
Result := count
end
make is
do
assert(foo = 1)
assert(bar = 1)
end
count: INTEGER
Further Aspects
- once is not applicable to attributes
- once "manifest string"
- once per object (other eiffel compilers have once ("OBJECT") to execute the feature body once per object) in Liberty there are no plans to implement such a feature