CODEWITHSUNDEEP
lua
x-x
x-x

Reputation: 7515

In Lua, how can you print the name of the current function, like the C99 __func__ identifier?

Something like this:

function foo()
    print( __func__ )
   ...
end

How can it be done?

Upvotes: 20

Views: 36033

Answers (7)

Chris Becke
Chris Becke

Reputation: 36016

You can't. In lua, functions are values. So they don't have names. You might as well ask "what the name of 2" is. Just because some variable was assigned the value '2' doesn't make that variable the name of 2. Likewise "someFunc" is a variable - potentially one of many - that holds a particular function.

As per @Orouborus in the comments:

function f() end is just syntactical sugar for f = function () end

Whatever you are doing, whatever the other posts are helping you do, you can print out the name of the thing on the left, "f", but not the name of the thing on the right.

Upvotes: 13

Andy Yuan
Andy Yuan

Reputation: 458

function __FILE__() return debug.getinfo(2, 'S').source end
function __LINE__() return debug.getinfo(2, 'l').currentline end
function __FUNC__() return debug.getinfo(2, 'n').name end

function printlinefilefunc()
    print("Line at "..__LINE__()..", FILE at "..__FILE__()..", in func: "..__FUNC__())
end

Output:

Line at 8, FILE at @./andydebug.lua, in func: printlinefilefunc

Upvotes: 8

Деян Добромиров
Деян Добромиров

Reputation: 902

You can try:

local dbFunc = debug.getinfo(1) and debug.getinfo(1).name or ""

Info
Info["currentline"] = 1376
Info["source"] = "@.\mymod.lua"
Info["short_src"] = ".\mymod.lua"
Info["nups"] = 13
Info["isvararg"] = false
Info["what"] = "Lua"
Info["lastlinedefined"] = 1570
Info["func"] = function: 000000000030B440
Info["istailcall"] = false
Info["linedefined"] = 1375
Info["namewhat"] = "field"
Info["name"] = "ExportDB" <<--- See here the function name
Info["nparams"] = 4

debug.getinfo(1) Returns this structure of the current execution state of the active function in the stack.

If n is larger than the number of active functions in the stack, debug.getinfo() returns nil.

That's why you have to check if it exists before taking *.name and return an empty string if the information is not available

A it is called inside the ExportDB() function, it return its name

Upvotes: 1

Puppy
Puppy

Reputation: 146910

Functions don't necessarily have them. It's perfectly legal in Lua to create anonymous functions with no name- and call it, without assigning it one.

(function()
    print("in anonymous function!")
end)()

Is perfectly valid Lua. What name do you want to give that function?

Upvotes: 2

gwell
gwell

Reputation: 2753

While I agree with Ephraim's answer, that code will not always report the same name as pointed out by Chris Becke. When the function is assigned to another variable, the "name" would be changed.

Here is another alternative. It just uses a string to identify the function. This method solves the changing name problem, but introduces a maintenance issue. The string would need to be kept in sync with the function name with future refactorization.

function foo()
  local __func__ = "foo"
  print( __func__ )
  --...
end

Alternatively, if the location of the function is more important than the name, the following may be better. It will give a name to the function that is based on the source and line number.

function getfunctionlocation()
  local w = debug.getinfo(2, "S")
  return w.short_src..":"..w.linedefined
end

function foo()
  print(getfunctionlocation()) --> foo.lua:6
  --...
end

If the __func__ still seems better, and standard Lua is not important, then the Lua parser can be modified as it is in this example for __FILE__ and __LINE__.

Upvotes: 4

Ephraim
Ephraim

Reputation: 797

#!/usr/bin/lua

local function myFunc()
 print(debug.getinfo(1, "n").name);
end
myFunc()

Upvotes: 33

schot
schot

Reputation: 11268

Use the Debug Library. It provides a getinfo(func) function that returns a table with information about the function.

Upvotes: 3

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