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.NET Forum / Languages / Managed C++ / October 2005C++/CLI equivalent to as keyword?
How would this C# contruct be represented in C++/CLI? Or is it even possible? PolicyLevel level = (enumerator->Current) as PolicyLevel; Thanks, Karch > How would this C# contruct be represented in C++/CLI? Or is it even > possible? > > PolicyLevel level = (enumerator->Current) as PolicyLevel; PolicyLevel* level=dynamic_cast<PolicyLevel*>(enumerator->Current); The equivalent of a cast in C# is __try_cast. Arnaud MVP - VC adebaene@club-internet.fr schrieb: >>How would this C# contruct be represented in C++/CLI? Or is it even >>possible? [quoted text clipped - 7 lines] > Arnaud > MVP - VC is __try_cast c++/CLI or managed c++ ? Or both ? > is __try_cast c++/CLI or managed c++ ? Or both ? Managed C++. For C++/CLI, use safe_cast : Check MSDN for details (a.k.a. RTFM) Arnaud MVP - VC dynamic_cast is the equivalent to the C# "as". static_cast is the equivalent in 2003 to basic C# casting (__try_cast is strictly 2003, but is more of a development tool, not a production casting technique). safe_cast is the equivalent to basic C# casting in CLI.  SignatureDavid Anton www.tangiblesoftwaresolutions.com Instant C#: VB.NET to C# Converter Instant VB: C# to VB.NET Converter Instant C++: C# to C++ Converter Instant J#: VB.NET to J# Converter > > How would this C# contruct be represented in C++/CLI? Or is it even > > possible? [quoted text clipped - 7 lines] > Arnaud > MVP - VC > dynamic_cast is the equivalent to the C# "as". > > static_cast is the equivalent in 2003 to basic C# casting (__try_cast is > strictly 2003, but is more of a development tool, not a production casting > technique). Why a "developement tool"? It gives you exactly the same behaviour as C# casting, whereas static_cast result is undefined if the cast is invalid. static_cast documentation for MC++ states explictely : "Unchecked pointer casts can break the type safety of __gc pointers, and cause the garbage collector to fail." Arnaud MVP - VC In 'Managed C++ and .NET Development', Stephen Fraser gives a good explanation for why you should regard __try_cast as a development tool - basically, __try_cast exceptions will only occur if there are actual mistakes in your code. But perhaps this is also close to what C# does. SignatureDavid Anton www.tangiblesoftwaresolutions.com Instant C#: VB.NET to C# Converter Instant VB: C# to VB.NET Converter Instant C++: C# to C++ Converter Instant J#: VB.NET to J# Converter > > dynamic_cast is the equivalent to the C# "as". > > [quoted text clipped - 10 lines] > Arnaud > MVP - VC > In 'Managed C++ and .NET Development', Stephen Fraser gives a good > explanation for why you should regard __try_cast as a development > tool - basically, __try_cast exceptions will only occur if there are > actual mistakes in your code. We agree; that's the wole point : It's better to have an exception that unmanaged behaviour and GC failure. Of course, it's still better to have an error at build time, but you don't always have what you want ;-) Now, if you are *really* performance worried (as much C++ developpers are, generally without any measurement to prove that their worries are justified ;-), you can replace __try_cast by static_cast and *pray* not to have an unnoticed invalid cast that will break hell loose in front of the client. > But perhaps this is also close to what > C# does. AFAIK, __try_cast and C# casts do strictly the same thing. Arnaud MVP - VC Good point Arnaud. It's apparent that we need to change conversion of the basic C# cast to use __try_cast for the 2003 target. (It's in today's build). Our conversion to the CLI target is correct in using safe_cast. SignatureDavid Anton www.tangiblesoftwaresolutions.com Instant C#: VB.NET to C# Converter Instant VB: C# to VB.NET Converter Instant C++: C# to C++ Converter Instant J#: VB.NET to J# Converter > > In 'Managed C++ and .NET Development', Stephen Fraser gives a good > > explanation for why you should regard __try_cast as a development [quoted text clipped - 15 lines] > Arnaud > MVP - VC >> In 'Managed C++ and .NET Development', Stephen Fraser gives a good >> explanation for why you should regard __try_cast as a development [quoted text clipped - 16 lines] > Arnaud > MVP - VC __try_cast (MC++) is recast into safe_cast ( C++/CLI) , both generate exactly the same IL instruction (castclass) just like an ordinary cast in C#. Willy. See : - How to: Implement is and as C# Keywords in C++ http://msdn2.microsoft.com/en-us/library/85af44e9 SignatureRegards, Nish [VC++ MVP] > How would this C# contruct be represented in C++/CLI? Or is it even > possible? [quoted text clipped - 3 lines] > Thanks, > Karch Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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