3 ms·

I wish that elixir had some syntax to simplify variable rebinding when returning from an if statement (as opposed to an if else). For example, some way to say l

I wish that elixir had some syntax to simplify variable rebinding when returning from an if statement (as opposed to an if else). For example, some way to say leave the variable unchanged if the if statement is false instead of having to clutter up the program with one line else clauses. Eg. myvar = 5 myvar = if somepredicate() do 200 end Will currently assign None to myvar if somepredicate is false.

phanimahesh 3y ago
I prefer explicit readability. Alternatives I can think of are unappealing.
Dowwie 3y ago
myvar = 5 myvar = if somepredicate() do 200 else myvar end
- lkuty 3y ago
  The wish of the OP is to avoid writing "else myvar". You could write a macro I guess. Something like the one below. Not that I have named the macro cond_assign for conditional assignment but there is no real assignement in Elixir, it is the match operator. Here we restrict its usage to "assignment" so expr1 should be a variable. defmodule OurMacro do defmacro cond_assign(expr1, expr2, do: block) do quote do unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1) end end end iex> import OurMacro OurMacro iex> myvar = 5 5 iex> cond_assign myvar, false, do: 200 5 iex> myvar 5 iex> cond_assign myvar, true, do: 200 200 iex> myvar 200
  - lkuty 3y ago
    Here is a better version that checks if expr1 is a variable. The condition "is_atom(x)" might be too strong. defmodule OurMacro do defmacro cond_assign(expr1, expr2, do: block) do case expr1 do {x, _, y} when is_atom(x) and is_atom(y) -> nil _ -> :erlang.error(RuntimeError.exception("The lvalue is not a variable: #{Macro.to_string(expr1)}")) end quote do unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1) end end end
jonnycat 3y ago
There are a couple of options to simplify and emulate a ternary operator: if x, do: y, else: z Or, though it's not very idiomatic Elixir, this also works: x && y || z
- te_chris 3y ago
  The binary matching is relatively idiomatic in liveview - check the CoreComponents files.
peoplefromibiza 3y ago
if you're writing Elixir code you'll find that most of the times the assignment is close to where you need the variable, so you usually end up writing something along the line of var = if x, do: 200, else: 5

phanimahesh 3y ago

I prefer explicit readability. Alternatives I can think of are unappealing.

Dowwie 3y ago

myvar = 5 myvar = if somepredicate() do 200 else myvar end

lkuty 3y ago
The wish of the OP is to avoid writing "else myvar". You could write a macro I guess. Something like the one below. Not that I have named the macro cond_assign for conditional assignment but there is no real assignement in Elixir, it is the match operator. Here we restrict its usage to "assignment" so expr1 should be a variable. defmodule OurMacro do defmacro cond_assign(expr1, expr2, do: block) do quote do unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1) end end end iex> import OurMacro OurMacro iex> myvar = 5 5 iex> cond_assign myvar, false, do: 200 5 iex> myvar 5 iex> cond_assign myvar, true, do: 200 200 iex> myvar 200
- lkuty 3y ago
  Here is a better version that checks if expr1 is a variable. The condition "is_atom(x)" might be too strong. defmodule OurMacro do defmacro cond_assign(expr1, expr2, do: block) do case expr1 do {x, _, y} when is_atom(x) and is_atom(y) -> nil _ -> :erlang.error(RuntimeError.exception("The lvalue is not a variable: #{Macro.to_string(expr1)}")) end quote do unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1) end end end

jonnycat 3y ago

There are a couple of options to simplify and emulate a ternary operator: if x, do: y, else: z Or, though it's not very idiomatic Elixir, this also works: x && y || z

te_chris 3y ago
The binary matching is relatively idiomatic in liveview - check the CoreComponents files.

peoplefromibiza 3y ago

if you're writing Elixir code you'll find that most of the times the assignment is close to where you need the variable, so you usually end up writing something along the line of var = if x, do: 200, else: 5