c# - Why does IEnumerator<T> inherit from IDisposable while the non-generic IEnumerator does not? -

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i noticed generic ienumerator<t> inherits idisposable, non-generic interface ienumerator not. why designed in way?

usually, use foreach statement go through ienumerator<t> instance. generated code of foreach has try-finally block invokes dispose() in finally.

basically oversight. in c# 1.0, foreach never called dispose 1. c# 1.2 (introduced in vs2003 - there's no 1.1, bizarrely) foreach began check in finally block whether or not iterator implemented idisposable - had way, because retrospectively making ienumerator extend idisposable have broken everyone's implementation of ienumerator. if they'd worked out it's useful foreach dispose of iterators in first place, i'm sure ienumerator have extended idisposable.

when c# 2.0 , .net 2.0 came out, however, had fresh opportunity - new interface, new inheritance. makes more sense have interface extend idisposable don't need execution-time check in block, , compiler knows if iterator ienumerator<t> can emit unconditional call dispose.

edit: it's incredibly useful dispose called @ end of iteration (however ends). means iterator can hold on resources - makes feasible to, say, read file line line. iterator blocks generator dispose implementations make sure finally blocks relevant "current point of execution" of iterator executed when it's disposed - can write normal code within iterator , clean-up should happen appropriately.

1 looking @ 1.0 spec, specified. haven't yet been able verify earlier statement 1.0 implementation didn't call dispose.


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