# Designs to reconsider
## References and move
Currently, we build Exprs by moving operands into the Expr structure. Consider using instead references:
- PROS:
- Smaller memory use per expression
- Resuse same sub-expression without copying
- Won't have to clone operands.
- CONS:
- Less clean syntax,
- More complicated lifetimes of expressions, especially in the helper
functions for things like multiplication and addition