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Version: 7.0

JOIN operator

The JOIN operator creates a property that implements a composition.

Syntax​

[JOIN] mainProperty(expr1, ..., exprN)

Where mainProperty is defined as:

propertyId

"[" operator "]"

"[" expression "]"

Where "[" and "]" are ordinary brackets.

Description​

When the main property is given in brackets — as a context-independent property operator or an expression — the property is built anonymously at the place of use, so an intermediate property need not be declared via the = statement.

An operator or expression in brackets may reference external parameters; the parameters of the resulting anonymous property follow the same rules as a property defined with = without explicit parameters.

Parameters​

  • propertyId

    Property ID of an existing property.

  • operator

    A context-independent property operator in brackets.

  • expression

    An expression in brackets.

  • expr1, ..., exprN

    List of expressions supplying the arguments of the main property. The number of expressions must equal the main property's parameter count; the list is empty when the main property has no parameters.

Examples​

f = DATA INTEGER (INTEGER, INTEGER, INTEGER);
g = DATA INTEGER (INTEGER, INTEGER);
h = DATA INTEGER (INTEGER, INTEGER);
c(a, b) = f(g(a, b), h(b, 3), a);

count = DATA BPSTRING[255] (INTEGER);
name = DATA BPSTRING[255] (INTEGER);
formatted(INTEGER a, INTEGER b) = [FORMULA BPSTRING[255] ' CAST($1 AS TEXT) || \' / \' || CAST($2 AS TEXT)'](count(a), name(b));

Sometimes it’s convenient to define the main property with an expression to simplify the source code and make it more understandable.

CLASS Triangle;
cathetus1 = DATA DOUBLE(Triangle);
cathetus2 = DATA DOUBLE(Triangle);

hypotenuseSq(triangle) = cathetus1(triangle)*cathetus1(triangle) + cathetus2(triangle)*cathetus2(triangle);

// a similar property set using composition
hypotenuseSq2(triangle) = [ x*x + y*y](cathetus1(triangle), cathetus2(triangle));