src/swipl-devel/packages/xpce/man/refmanual/md/assign.md

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class assign {#class-assign}

Class assign defines an assignment statement for a var object. An assign is an executable object that, when executed, evaluates its <-value and assigns its <-var with this value. See class var for a discussion on variables and assignments (var ->assign).

Class assign is first of all introduced for syntactical cosmetical reasons. The following two code objects perform the same function:

assign(Var, Value).
message(Var, assign, Value).

An assign object demands its first argument to be an instance of class var. This implies that named variables can be referred to much more elegant. Executing

assign(x, 10)

Will assign 10 to the variable named x, while the message variant would be:

message(?(@variables, member, x), assign, 10)

See also <-convert.

@see class var

Instance variables {#class-assign-instvars}

• assign<->scope: {local,outer,global} Scope of the assignment. See var ->assign for the interpretation of the scope names. The default is local.

• assign<->value: any|function Value to assign to the variable. In many cases this will be a function object, which is executed by the assign object when it is ->_execute'd.

• assign<->var: var Var object to assign. See also <-value and var ->assign.

Send methods {#class-assign-send}

• assign->_execute The execution of an assign object implies

  1. Evaluate <-value if this is a function object.

  2. var ->assign the <-var with the result of 1).

• assign->initialise: variable=var, value=any|function, scope=[{local,outer,global}] Create a var object from the <-var, <-value and <-scope.

rswipl documentation built on June 16, 2026, 5:07 p.m.