When developing & debugging, I sometimes wish I could write a 1-liner that dumped the names, types & values of a bunch of variables. The problem is I don't know how to access the name of a variable, if I can at all.
Here is a first attempt:
foo = 1
bar = "42"
baz = Hash.new
[开发者_如何学运维foo, bar, baz].each do |v|
puts "#{v.???} = (#{v.class}) #{v}"
end
I'd like the output of this program to be something like:
foo = (Fixnum) 1
bar = (String) 42
baz = (Hash) ...
I don't know what ???
should be above. Can this be done?
foo = 1
bar = "42"
baz = Hash.new
%w(foo bar baz).each do |vn|
v = eval(vn)
puts "#{vn} = (#{v.class}) #{v}"
end
But this, of course, doesn't help you if you want a method with 1 argument.
Here's a little bit of debug code I use all over the place (I stick it in a separate file so that it can be required wherever needed). It can be used two ways. Passed one or more values, it simply inspects them and writes the result to $stderr. But passed a block which returns one or more things, it writes them out with their names.
#!/usr/bin/ruby1.8
def q(*stuff, &block)
if block
s = Array(block[]).collect do |expression|
value = eval(expression.to_s, block.binding).inspect
"#{expression} = #{value}"
end.join(', ')
$stderr.puts s
else
stuff.each do
|thing| $stderr.print(thing.inspect + "\n")
end
end
end
i = 1
q i # => 1
q {:i} # => i = 1
name = "Fred"
q [name, name.length] # => ["Fred", 4]
q {[:name, 'name.length']} # => name = "Fred", name.length = 4
Note: The q
function, and more, is now available in the cute_print gem.
No, because foo
/bar
/baz
are not instance variables in your code. They are local variables (instance variables start with a @
). There is a way to do it with instance variables and the Object#instance_variables
method, though:
@foo = 1
@bar = 2
@baz = 3
instance_variables.each do |var|
value = instance_variable_get var
puts "#{var} = (#{value.class}) #{value}"
end
# outputs:
# @foo = (Fixnum) 1
# @bar = (Fixnum) 2
# @baz = (Fixnum) 3
To get the name of a particular instance variable, loop through all of the instance variables until you find one with a value that matches your instance variable.
foo = 1
bar = "42"
baz = Hash.new
Varspec = Struct.new(:name, :type, :value, :inspect_str) do
def to_s
"#{name} = (#{type}) #{inspect_str}"
end
end
lvars = local_variables.map {|lvar|
lvar = lvar.to_s
val = eval(lvar)
val = val.dup rescue val
Varspec.new(lvar, val.class, val, val.inspect)
}
puts lvars
# baz = (Hash) {}
# bar = (String) "42"
# foo = (Fixnum) 1
Or, you could just use a debugger. That's what they were invented for, after all.
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