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Parameter Definitions

Describes the structure of a parameter definition.

Introduction

A parameter definition defines a constant value available to all objects of a given class. When you create a class definition (or at any point before compilation), you can set the values for its class parameters. By default, the value of each parameter is the null string, but you can specify a non-null value as part of the parameter definition. At compile-time, the value of the parameter is established for all instances of a class. With rare exceptions, this value cannot be altered at runtime.

Details

A parameter definition has the following structure:

/// description Parameter name As parameter_type [ keyword_list ] = value ;

Where:

  • description (optional) is intended for display in the Class Reference. The description is blank by default. See “Creating Class Documentation” in Using Caché Objects.

  • name (required) is the name of the parameter. This must be a valid class member name, and must not conflict with any other class member names.

  • parameter_type (optional) specifies the user interface type of the parameter.

    This is not a class name; see the next section. This information is intended for use by development tools, to assist the developer who provides a value for the parameter in a subclass. In most cases, the compiler ignores this keyword.

    If you omit parameter_type, also omit the word As

  • value (optional) specifies the value of the parameter. If you omit value, also omit the equals sign =

  • keyword_list (optional) is a comma-separated list of keywords that further define the parameter.

    See the section “Parameter Keywords.”

    If this list is omitted, also omit the square brackets.

Allowed Types for Parameters

The parameter_type option can be one of the following values:

  • BOOLEAN — A true (1) or false (0) value.

  • CLASSNAME — A valid class name.

  • COSCODE — ObjectScript code.

  • COSEXPRESSION — A valid ObjectScript expression.

    If a parameter is of type COSEXPRESSION, the expression is evaluated at runtime.

    Unlike most other values of the parameter Type keyword, this value affects the compiler.

  • COSIDENTIFIER — A valid ObjectScript identifier.

  • INTEGER — An integer value.

  • SQL — An SQL statement.

  • SQLIDENTIFIER — A valid SQL identifier.

  • STRING — A string value.

  • TEXT — A multi-line text value.

  • CONFIGVALUE — A parameter that can be modified outside of the class definition. Unlike most other values of the parameter Type keyword, this value affects the compiler. If a parameter is of type CONFIGVALUE, then you can modify the parameter via the $SYSTEM.OBJ.UpdateConfigParam(). For example, the following changes the value of the parameter MYPARM (in the class MyApp.MyClass so that its new value is 42:

    set sc=$system.OBJ.UpdateConfigParam("MyApp.MyClass","MYPARM",42)
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    Note that $SYSTEM.OBJ.UpdateConfigParam() affects the generated class descriptor as used by any new processes, but does not affect the class definition. If you recompile the class, Caché regenerates the class descriptor, which will now use the value of this parameter as contained in the class definition (thus overwriting the change made via $SYSTEM.OBJ.UpdateConfigParam()).

You also can omit parameter_type, in which case Studio will allow any value for the parameter.

Example

/// This is the name of our web service.
Parameter SERVICENAME = "SOAPDemo" ;
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See Also