[OASIS Issue Tracker] (ODATA-953) Consider deprecating structural casting

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

     [ https://issues.oasis-open.org/browse/ODATA-953?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Pizzo updated ODATA-953:
--------------------------------

    Environment: [Proposed]
    Description: 
Section 5.1.1.8.1, cast, of [URL Conventions] currently says that the cast function can be used to cast to types outside of a type hierarchy using structural casting--whatever names (and types) match are cast to the new type:

•	Services MAY support structural casting of entities and complex type instances to a derived type, or arbitrary structured type, by assigning values of identically named properties and casting them recursively. The cast fails if one of the property-value casts fails or the target type contains non-nullable properties that have not been assigned a value.

Minimally, we need to clarify that this only applies to the cast function and not appending a cast segment, i.e., to a collection, since we count on appending cast segments to filter the collection according to those types that are of the particular type.

We could go one step further and deprecate the structural casting from the cast function as something that seemed like a safe enough thing at the time but turned out not to be a great idea. 
       Proposal: Clarify that structural casting MUST NOT be applied anywhere other than the explicit cast operator; i.e., it MUST NOT be applied when using cast segments nor evaluating isof.

> Consider deprecating structural casting
> ---------------------------------------
>
>                 Key: ODATA-953
>                 URL: https://issues.oasis-open.org/browse/ODATA-953
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: Bug
>          Components: OData URL Conventions
>    Affects Versions: V4.0_ERRATA03
>         Environment: [Proposed]
>            Reporter: Michael Pizzo
>             Fix For: V4.01_WD01
>
>
> Section 5.1.1.8.1, cast, of [URL Conventions] currently says that the cast function can be used to cast to types outside of a type hierarchy using structural casting--whatever names (and types) match are cast to the new type:
> •	Services MAY support structural casting of entities and complex type instances to a derived type, or arbitrary structured type, by assigning values of identically named properties and casting them recursively. The cast fails if one of the property-value casts fails or the target type contains non-nullable properties that have not been assigned a value.
> Minimally, we need to clarify that this only applies to the cast function and not appending a cast segment, i.e., to a collection, since we count on appending cast segments to filter the collection according to those types that are of the particular type.
> We could go one step further and deprecate the structural casting from the cast function as something that seemed like a safe enough thing at the time but turned out not to be a great idea. 



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