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Christoph Rabel
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 Posted: Thu Aug 21, 2003 5:18 am Post subject: Why ist there no const version of operator[] for map? |
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Hi!
I wonder where there is no const counterpart to the existing version.
I recently stumbled on that problem when writing a getValue(Key)
Function that I declared as const. I couldnt use operator[] to get the
value but had to use find().
Is there any harm in adding this function?
thx for any insights,
Christoph
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James Dennett
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| Posted: Thu Aug 21, 2003 9:31 am Post subject: Re: Why ist there no const version of operator[] for map? |
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Christoph Rabel wrote:
| Quote: | Hi!
I wonder where there is no const counterpart to the existing version.
I recently stumbled on that problem when writing a getValue(Key)
Function that I declared as const. I couldnt use operator[] to get the
value but had to use find().
Is there any harm in adding this function?
thx for any insights,
|
This has been covered a number of times in the past;
a search of the archives through Google Groups might
well dig up repeated discussions.
In a nutshell:
(a) There is none because the convenience of having
operator[] automatically add values if they are absent
was chosen
(b) It is unacceptable to many for a const version to
behave differently than a non-const version, except in
const-ness, so a const operator[] cannot be added.
You can write a function to get an element from a map,
but you'll need to decide what it should do if the element
is absent. You'll just have to choose a name for the
function: the name operator[] has already been taken for
a function with different semantics.
-- James.
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