newClass -- set the class and parent of an object

common remarks

If x is a basic list or sequence, then BasicList should be an ancestor of A and B should be Nothing. If x is a hash table, then HashTable should be an ancestor of A.

If the class (and parent) of x are already equal to A (and B, respectively), then copying of the elements of x is not required, and is not done.

If x is mutable, and instances of class A are also mutable, then copying of the elements of x is not required, and is not done.

If x is not a hash table, basic list, or sequence, then its class will be set to A internally, essentially by wrapping it in a special kind of object designed solely to indicate the new class. The new class A must be a specialization of the class of x. The parent cannot be reset this way. Not all of the internal code of Macaulay 2 is ready to recognize such wrapped objects, which are part of a new feature, except for the code that handles functions.

i1 : t = 1..4

o1 = (1, 2, 3, 4)

o1 : Sequence

i2 : newClass(Array,t)

o2 = [1, 2, 3, 4]

o2 : Array

i3 : x = new HashTable from { a => 1, b => 2 }

o3 = HashTable{a => 1}
               b => 2

o3 : HashTable

i4 : z = newClass(ImmutableType,Vector,x)

o4 = ImmutableType{a => 1}
                   b => 2

o4 : ImmutableType

i5 : parent z

o5 = Vector

o5 : Type

The difference between new A of B from x and newClass(A,B,x) is that the methods installed for new are not used.

i6 : new Thing of Thing from Thing := (A,B,c) -> (
            << "-- new " << A << " of " << B 
            << " from " << toString c << endl;
            c);

i7 : new ImmutableType of Vector from x
-- new ImmutableType of Vector from new HashTable from {a => 1, b => 2}

o7 = ImmutableType{a => 1}
                   b => 2

o7 : ImmutableType

i8 : newClass(ImmutableType,Vector,x)

o8 = ImmutableType{a => 1}
                   b => 2

o8 : ImmutableType