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Field Assignment

rascal-0.40.17

Synopsis​

Assignment to a field of a tuple or datatype.

Syntax​

Exp₁ [ FieldName = Exp₂ ]

Description​

Exp₁ should evaluate to a tuple or a constructor with a field named Name. Statically the type should either be a assign the value of Exp₂ to that field

Field assignment applies to all values that have named components like tuples and constructors with named elements, and locations. Field assignment returns a new value in which the named component has been replaced by a new value. Name stands for itself and is not evaluated.

Examples​

rascal>node T = "name"(1, x="abc");
node: "name"(1,
  x="abc")
rascal>T[x = "def"];
node: "name"(1,
  x="def")
rascal>T
node: "name"(1,
  x="abc")
rascal>T = T[x="def"];
node: "name"(1,
  x="def")
rascal>T
node: "name"(1,
  x="def")

Observe that field assignment creates a new value with an updated field. The old value remains unchanged as can be seen from the unchanged value of T in the above example.