Module show_notes::e005

Allocate it where?

• Date: November 8, 2015
• Subject: Returning functions from other functions, and thinking about the stack, the heap, and reference types.
• Audio

Notes

This episode, we look at returning functions from other functions, and as part of that discuss some basics about the stack and the heap---and why we need to care about them for returning functions.

The functions themselves are not especially interesting; they just show you the basic form you use to return functions from other functions, and how to then use them in another function. You'll want to take a detailed look instead at the documentation for each (or just read the source!), because that's where the meat of the discussion in this week's code is.

Corrigenda

• Steve Klabnik pointed out that my description of Vector types as totally heap-allocated was misleading. It's better to say that the contents of the Vector -- its data -- is heap-allocated, while the memory for the smart pointer and associated metadata are allocated on the stack. I had this in mind, and sort of alluded to it earlier in the discussion, but the way I actually said it was misleading at best.

• Chad Sharp (@crossroads1112 on GitHub) clarified that in C99, C does support dynamic array allocation, though it became optional for compilers to implement it as of C11. I forgot about this because I spend so much of my time dealing with Visual C++, which does not support dynamic array allocation. (Notably, Visual C does; it is Visual C++ which does not: remember, C and C++ are related but distinct languages.)

Thanks to Steve and Chad for their helpful feedback!

Links

• Rust 1.4 release announcement
• "Clarify (and improve) rules for projections and well-formedness"
• MSVC support tracking issue
• Rust 1.4 full release notes
• "What and where are the stack and the heap?"

Sponsors

• reddraggone9
• Chris Patti

Become a sponsor

• Patreon
• Venmo
• Dwolla
• Cash.me

Follow

• New Rustacean:
  • Twitter: @newrustacean
    • App.net: @newrustacean
  • Email: [email protected]
• Chris Krycho
  • Twitter: @chriskrycho
    • App.net: @chriskrycho

Functions

demonstrate_function_returns	Uses the doubler_factory to get a function which doubles a number.
doubler_closure_factory	Creates a closure which doubles an integer.
doubler_factory	Creates a function which doubles an integer.