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POstill confused about covariance and contravariance & in/out
 

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  1. POstill confused about covariance and contravariance & in/out
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    <p>ok i read a bit on this topic on stackoverflow, watched <a href="http://msdn.microsoft.com/en-us/vcsharp/ee672319.aspx" rel="nofollow noreferrer">this</a> &amp; <a href="http://channel9.msdn.com/posts/bruceky/Whirlwind-13-Whats-new-in-C-4-Covariance--Contravariance/" rel="nofollow noreferrer">this</a>, but still a bit confused about co/contra-variance. </p> <p>from <a href="https://stackoverflow.com/questions/1078423/c-is-variance-covariance-contravariance-another-word-for-polymorphism/1078469#1078469">here</a></p> <blockquote> <p>Covariance allows a "bigger" (less specific) type to be substituted in an API where the original type is only used in an "output" position (e.g. as a return value). Contravariance allows a "smaller" (more specific) type to be substituted in an API where the original type is only used in an "input" position.</p> </blockquote> <p>i know it has to do with type safety. </p> <p>about the <code>in/out</code> thing. can i say i use <code>in</code> when i need to write to it, and <code>out</code> when its read only. and <code>in</code> means contra-variance, <code>out</code> co-variance. but from the explanation above... </p> <p>and <a href="https://stackoverflow.com/questions/1078423/c-is-variance-covariance-contravariance-another-word-for-polymorphism">here</a></p> <blockquote> <p>For example, a <code>List&lt;Banana&gt;</code> can't be treated as a <code>List&lt;Fruit&gt;</code> because <code>list.Add(new Apple())</code> is valid for List but not for <code>List&lt;Banana&gt;</code>.</p> </blockquote> <p>so shouldn't it be, if i were to use <code>in</code>/ am going to write to the object, it must be bigger more generic. </p> <p>i know this question has been asked but still very confused. </p>
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    1. USJiew Meng
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      1. USHamish Grubijan
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    1. COI am confused as well, After reading up on it at Wikipedia I feel like I need to take real analysis 1&2, followed by measure theory, vector spaces, and finally categorization theory before I get a good intuitive feel for it. Alternatively, if someone posts a bunch of examples, I can probably cut down the learning time from 5 semesters to 1 month.
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      1. USHamish Grubijan
    2. COPlease don't abbreviate here. The idea is to write in English, not to use things like "abt" and "abit".
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      1. USJohn Saunders
 

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