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Replaced references to assignment attempt with object test.

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Author:halw
Date:2012-04-13T13:54:19.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@1073 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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halw
2012-04-13 13:54:19 +00:00
parent 9bb540cab2
commit 7269a8a613
1 changed files with 2 additions and 2 deletions
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documentation/current/platform-specifics/microsoft-windows/com/eiffelcom-library/eiffelcom-interface-content/interfaces.wiki
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@@ -11,11 +11,11 @@ For each interface listed in a type library, the EiffelCOM wizard generates a de
==ECOM_QUERIABLE==
Different languages handle type coercion in different ways. C uses type cast; C++ introduces several type casting mechanisms; Eiffel uses assignment attempt, etc. Every COM interface exposes the <eiffel>QueryInterface</eiffel> function which allows clients to query the COM component for a pointer to another interface. Querying a component for an interface pointer is similar to using an assignment attempt in Eiffel. The Eiffel implementation of the assignment attempt relies on the runtime data. Since changing the Eiffel runtime and the implementation of the assignment attempt was not an option, EiffelCOM introduces a library class [[ref:libraries/com/reference/ecom_queriable_chart|ECOM_QUERIABLE]] , which has the creation routine
Different languages handle type coercion or type narrowing in different ways. C uses type cast; C++ introduces several type casting mechanisms; Eiffel uses [[ET: Inheritance#Object test|object test]], etc. Every COM interface exposes the <eiffel>QueryInterface</eiffel> function which allows clients to query the COM component for a pointer to another interface. Querying a component for an interface pointer is analogous to using an object test in Eiffel. To accomplish this, EiffelCOM introduces a library class [[ref:libraries/com/reference/ecom_queriable_chart|ECOM_QUERIABLE]], which has the creation routine
<code>
make_from_other (other: ECOM_INTERFACE)</code>
which queries a COM component internally. Every interface proxy class inherits from [[ref:libraries/com/reference/ecom_queriable_chart|ECOM_QUERIABLE]] . The one difference between this mechanism versus using assignment attempt is that upon failure an exception will be raised. An assignment attempt that fails simply returns <code>Void</code>.
which queries a COM component internally. Every interface proxy class inherits from [[ref:libraries/com/reference/ecom_queriable_chart|ECOM_QUERIABLE]]. An important difference between this mechanism and using an object test is that if the creation routine fails to initialize a new [[ref:libraries/com/reference/ecom_queriable_chart|ECOM_QUERIABLE]] object, an exception will be raised, whereas, the <eiffel>attached</eiffel> syntax of the object test will merely produce a <code>False</code> result in the case in which no object of the desired type is available.
==ECOM_STUB==