Reflection/Get source

Task

The goal is to get the source code or file path and line number where a programming object (e.g. module, class, function, method) is defined.

J

Source code which when executed will recreate the definition can be obtained using 5!:5 <'name' where name is the name of the thing you want source code for. Or, you can use 5!:6 which will provide a "fully parenthesized" variant for the tacit part of any definition.

You can also use 4!:4 and 4!:3 to find the file containing the name's definition (if there is one). Line number is not tracked.

Examples:

<lang J> mean=:+/ %#

  5!:5 <'mean'

+/ % #

  5!:6 <'mean'

(+/) % #

  4!:4 <'mean'

_1

  4!:4 <'names'

2

  2 { 4!:3

┌────────────────────────────────────────────┐ │/Applications/j64-804/system/main/stdlib.ijs│ └────────────────────────────────────────────┘</lang>

We could also provide convenience functions for these mechanisms:

<lang J> linrep=: 5!:5@<

  srcfile=: (4!:4@<) { a:,~ 4!:3 bind </lang>

Example use:

<lang J> linrep 'names' list_z_@nl

  srcfile 'names'

┌────────────────────────────────────────────┐ │/Applications/j64-804/system/main/stdlib.ijs│ └────────────────────────────────────────────┘

  srcfile 'mean'

┌┐ ││ └┘</lang>

JavaScript

Function.toString() will return the source code for user-defined functions.

<lang javascript>function foo() {...} foo.toString(); // "function foo() {...}" </lang>

For native functions, the function body typically will be a syntactically invalid string indicating the function is native. This behavior isn't part of any ECMAScript standard, but is common practice. <lang javascript>Math.sqrt.toString(); // "function sqrt() { [native code] }" </lang>

Python

Modules loaded from files have a __file__ attribute. <lang python>import os os.__file__

"/usr/local/lib/python3.5/os.pyc"

</lang>

Ruby

Method#source_location will return the file and line number of a Ruby method. If a method wasn't defined in Ruby, Method#source_location returns nil. <lang ruby>require 'mathn' Math.method(:sqrt).source_location

["/usr/local/lib/ruby2.3/2.3.0/mathn.rb", 119]

Class.method(:nesting).source_location

nil, since Class#nesting is native

</lang>