From: Fernando Cacciola (fcacciola_at_[hidden])
Date: 2002-01-23 15:03:50
----- Original Message -----
Sent: Wednesday, January 23, 2002 4:47 PM
Subject: Re: [boost] environment variable access
> >> What I'd like (and what I'm trying to implement in command
> >> parser) is map like interface. So that one could be able to say
> >> environment["http_proxy"].as<ip_address>()
> >> where "as" method is a shortcut to lexical_cast/any_cast.
> What about orthogonality?
VERY good point!
But I'm not sure if a plain string is right, tough.
If you want to check if the external variable is there, and only then get
it, you'll need two calls to the enviroment:
if ( exist_in_environment["http_proxy"] )
foo ( environment["http_proxy"] ) ;
AFAICT, this can be solved in 3 ways:
1) Return a proxy which holds the string and some way to test if it is
initialized, such as:
external_var a = environment["http_proxy"] ;
if ( !!a )
2) Honor orthogonbality by using the 'optional<>' class which I presented
some time ago:
optional<string> a = environment["http_proxy"] ;
if ( !!a )
This aproach requires operator  to return optional<string>.
3) Mimic the optional<> behaviour, cluttering the interface:
pair<string,bool> a = environment["http_proxy"] ;
if ( a.second )
This aproach requires operator  to return pair<string,bool>.
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