Dynamic vrs. Any

teotigraphix · February 18, 2021, 7:49pm

Hi,

I have been looking around for an exact definition of why these two are different, programming and compiler wise. ?

Gama11 · February 18, 2021, 8:00pm

HaxeFoundation/haxe-evolution/blob/master/proposals/0001-any.md#any-type

# Any type

* Proposal: [HXP-0001](0001-any.md)
* Author: [Dan Korostelev](https://github.com/nadako)
* Status: implemented in 3.3.0

## Introduction

Provide new toplevel type `Any` to be used for containing values of any type (hence the name)
as a safer alternative to `Dynamic`.

## Motivation

The current way to pass values of any type is typing them as `Dynamic`, but it's
very error-prone because `Dynamic` completely subverts type-safety and its behaviour
is weird in several ways:

 * Field access to `Dynamic` values yields `Dynamic` values as well, which actually makes sense,
   but also further spreads the untyped behaviour which leads to runtime-specific behaviour, like
   this famous example:

This file has been truncated. show original

teotigraphix · February 18, 2021, 8:03pm

Exactly, thanks!

teotigraphix · February 18, 2021, 8:18pm

For others; seems the real difference from that paper says Any has no dynamic field access.

This means any time(no pun intended) you use Any as a type, you have to explicitly cast to a concrete type before you can use fields of the hidden Any type after casting. eg (Field, Method access)

mark.knol · February 19, 2021, 8:50am

I think it’s best practice to:

try to type anything or leave it up to compiler or (if you have time) use macro’s to help to create the types
if that’s not possible, use Any as much as, or use things like haxe.DynamicAccess
and use Dynamic as last option because that disables all the goodness the compiler could give.

I think, unless you write a library or access external stuff outside your Haxe code, using things like Any/Dynamic aren’t needed.

teotigraphix · February 19, 2021, 1:48pm

I have been writing bindings for JS so sludge is inevitable with that translation.