Saklad5
January 1, 2022, 6:23pm
138
The performance roadmap has a start. Maybe if ref, or whatever it ends up being called?
Borrow variables
When working with deep object graphs, it’s natural to want to assign a local variable to a property deeply nested within the graph:
let greatAunt = mother.father.sister
greatAunt.sayHello()
greatAunt.sayGoodbye()
However, with shared mutable objects, such as global variables and class instances, these local variable bindings necessitate a copy of the value out of the object; either mother or mother.father above could be mutated by code anywhere else in the program referencing the same objects, so the value of mother.father.sister must be copied to the local variable greatAunt to preserve it independently of changes to the object graph from outside the local function. Even with value types, other mutations in the same scope would force the variable to copy to preserve the value at the time of binding. We may want to prevent such mutations while the binding is active, in order to be able to share the value in-place inside the object graph for the lifetime of the variable referencing it. We can do this by introducing a new kind of local variable binding that binds to the value in place without copying, while asserting a borrow over the objects necessary to access the value in place:
// `ref` comes from C#, as a strawman starting point for syntax.
// (It admittedly isn't a perfect name, since unlike C#'s ref, this would
// actively prevent mutation of stuff borrowed to form the reference, and
// if the right hand side involves computed properties and such, it may not
// technically be a reference)
ref greatAunt = mother.father.sister
greatAunt.sayHello()
mother.father.sister = otherGreatAunt // error, can't mutate `mother.father.sister` while `greatAunt` borrows it
greatAunt.sayGoodbye()
Changing the subject back, I firmly believe that explicitly naming optional bindings is important for code clarity. And if there’s disagreement on that front, it would be better to use shorthand arguments ($0, etc.) instead of implicit shadowing. It’s not like the latter would provide any further information.
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