Copies of constant objects should be modifiable.

[skx]

This code fails:

 let a = PI;
 let a = a.to_i();
 > Error: Attempting to modify 'a' denied; it was defined as a constant.

However this works:

let a = PI;
puts( a.to_i() );

The reason for this is the assignment-operation copies the const-value of the source variable (PI in this case).