Because printf is a method of Kernel
ratdog:~ mike$ irb
irb(main):001:0> x = 3
=> 3
irb(main):002:0> Kernel.printf('%X', x)
3=> nil
irb(main):003:0> 3.methods.include?('printf')
=> false
irb(main):004:0> Kernel.methods.include?('printf')
=> true
And for a Fixnum printf is indeed private:
ratdog:~ mike$ irb
irb(main):001:0> 3.private_methods
=> ["select", "lambda", "local_variables", "chomp", "raise", "sub!",
"Array", "print", "trap", "method_missing", "format", "exit!",
"at_exit", "readlines", "set_trace_func", "autoload", "system",
"getc", "initialize_copy", "split", "fail", "putc", "gsub!",
"iterator?", "catch", "p", "remove_instance_variable", "sleep",
"sub", "syscall", "callcc", "Integer", "fork", "srand",
"irb_binding", "singleton_method_removed", "caller", "chop!", "puts",
"scan", "autoload?", "binding", "block_given?", "throw", "warn", "`",
"gsub", "loop", "Float", "open", "singleton_method_undefined",
"rand", "exit", "chomp!", "gets", "trace_var", "load", "exec",
"global_variables", "proc", "initialize", "chop", "printf", "String",
"test", "sprintf", "abort", "readline", "untrace_var", "require",
"eval"]
--
Mike Stok <
[email protected]>
http://www.stok.ca/~mike/
The "`Stok' disclaimers" apply.