method

trace_var

v1_8_7_72 - Show latest stable - 0 notes - Class: Kernel

trace_var(...) public

Controls tracing of assignments to global variables. The parameter +symbol_ identifies the variable (as either a string name or a symbol identifier). cmd (which may be a string or a Proc object) or block is executed whenever the variable is assigned. The block or Proc object receives the variable’s new value as a parameter. Also see Kernel::untrace_var.

   trace_var :$_, proc {|v| puts "$_ is now '#{v}'" }
   $_ = "hello"
   $_ = ' there'

produces:

   $_ is now 'hello'
   $_ is now ' there'

Show source

/*
 *  call-seq:
 *     trace_var(symbol, cmd )             => nil
 *     trace_var(symbol) {|val| block }    => nil
 *  
 *  Controls tracing of assignments to global variables. The parameter
 *  +symbol_ identifies the variable (as either a string name or a
 *  symbol identifier). _cmd_ (which may be a string or a
 *  +Proc+ object) or block is executed whenever the variable
 *  is assigned. The block or +Proc+ object receives the
 *  variable's new value as a parameter. Also see
 *  <code>Kernel::untrace_var</code>.
 *     
 *     trace_var :$_, proc {|v| puts "$_ is now '#{v}'" }
 *     $_ = "hello"
 *     $_ = ' there'
 *     
 *  <em>produces:</em>
 *     
 *     $_ is now 'hello'
 *     $_ is now ' there'
 */

VALUE
rb_f_trace_var(argc, argv)
    int argc;
    VALUE *argv;
{
    VALUE var, cmd;
    struct global_entry *entry;
    struct trace_var *trace;

    rb_secure(4);
    if (rb_scan_args(argc, argv, "11", &var, &cmd) == 1) {
	cmd = rb_block_proc();
    }
    if (NIL_P(cmd)) {
	return rb_f_untrace_var(argc, argv);
    }
    entry = rb_global_entry(rb_to_id(var));
    if (OBJ_TAINTED(cmd)) {
	rb_raise(rb_eSecurityError, "Insecure: tainted variable trace");
    }
    trace = ALLOC(struct trace_var);
    trace->next = entry->var->trace;
    trace->func = rb_trace_eval;
    trace->data = cmd;
    trace->removed = 0;
    entry->var->trace = trace;

    return Qnil;
}

trace_var

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