Thomas Linder Puls: release

2019-03-12T16:13:39Z

release

← Older revision		Revision as of 18:13, 12 March 2019
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	This section describes how to define attributes that can be written on entities in a program. Currently, the attributes will not have any semantics influence nor can they be accessed through reflection, so they will only be accessible to tools that parse the code itself.		This section describes how to define attributes that can be written on entities in a program. Currently, the attributes will not have any semantics influence nor can they be accessed through reflection, so they will only be accessible to tools that parse the code itself.

Thomas Linder Puls: initial version

2019-02-13T13:15:56Z

initial version

New page

{{Template:NonReleased}}

This section describes how to define attributes that can be written on entities in a program. Currently, the attributes will not have any semantics influence nor can they be accessed through reflection, so they will only be accessible to tools that parse the code itself.

{{Example|1=As an example consider the use of the attributes <vp>meta</vp> and <vp>metaDisplayAs</vp>

<vip>
interface person supports personGenerated
[meta]

properties
name : string [meta].
address : string [metaDisplayAs("address")].

end interface person
</vip>

The basic idea is that an external tool parses the file (in an external step) and based on the code and the meta attributes generates the interface (+ class + implementation) <vp>personGenerated</vp>. The exact contents of the generated class is not relevant for this example; the important thing is that the attributes are used to define what should be generated and how it should function.
}}

Without any further action the compiler will generate warnings for the attributes above. To avoid this the attributes can be defined in a functor domain which is given the attribute <vp>attribute</vp>:

<vip>
namespace ns

interface meta

domains
meta =
meta;
metaDisplayAs(string DisplayAs) [attribute].

end interface meta
</vip>

Notice that the attributes are both in a namespace and a scope.

Using normal rules that will handle name conflicts. On the other hand the <vp>person</vp> interface will use to qualified attributes:

<vip>
interface person supports personGenerated
[ns\meta::meta]

properties
name : string [ns\meta::meta].
address : string [ns\meta::metaDisplayAs("address")].

end interface person
</vip>

The qualification can be omitted by opening the scope

<vip>
interface person supports personGenerated
open ns\meta
[meta]

properties
name : string [meta].
address : string [metaDisplayAs("address")].

end interface person
</vip>

Given this the compiler will:

* suppress the w193 warning (for unknown attribute)
* resolve ambiguities (when everybody want to use <vp>meta</vp> and <vp>test</vp> as attribute names)
* type check the attributes

The attributes will have to follow the rules for (compile time computable) constants (i.e. cannot contain function and predicate calls).

[[Category:Tutorials|{{PAGENAME}}]]

Program Defined Attributes - Revision history

Thomas Linder Puls: release

Thomas Linder Puls: initial version