Why are mutables allowed in F#? When are they essential? -


coming c#, trying head around language.

from understand 1 of main benefits of f# ditch concept of state, should (in many cases) make things more robust.

if case (and correct me if it's not), why allow break principle mutables? me feels don't belong in language. understand don't have use them, gives tools go off track , think in oop manner.

can provide example of mutable value essential?

current compilers declarative (stateless) code not smart. results in lots of memory allocations , copy operations, rather expensive. mutating property of object allows re-use object in new state, faster.

imagine make game 10000 units moving around @ 60 ticks second. can in f#, including collisions mutable quad- or octree, on single cpu core.

now imagine units , quadtree immutable. compiler have no better idea allocate , construct 600000 units per second , create 60 new trees per second. , excludes changes in other management structures. in real-world use case complex units, kind of solution slow.

f# multi-paradigm language enables programmer write functional, object-oriented, and, extent, imperative programs. currently, each variant has valid uses. maybe, @ point in future, better compilers allow better optimization of declarative programs, right now, have fall imperative programming when performance becomes issue.


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