{"id":117,"date":"2011-06-22T16:39:52","date_gmt":"2011-06-22T20:39:52","guid":{"rendered":"http:\/\/www.joshmatthews.net\/blog\/?p=117"},"modified":"2011-06-24T15:02:23","modified_gmt":"2011-06-24T19:02:23","slug":"nscomptr-has-never-been-so-pretty","status":"publish","type":"post","link":"https:\/\/www.joshmatthews.net\/blog\/2011\/06\/nscomptr-has-never-been-so-pretty\/","title":{"rendered":"nsCOMPtr has never been so pretty"},"content":{"rendered":"

Jim Blandy announced his archer-mozilla<\/a> pretty-printers for Spidermonkey late last year. I’ve used them a few times while working on some JS proxy bugs, and I’ve found them to be invaluable. So invaluable, in fact, that I’ve written a bunch of pretty-printers for some pain points outside of js\/. If this prospect excites you so much that you can’t be bothered to read the remaining examples, you can acquire the code from its hg repo<\/a>. Please note, you’ll need to be using gdb >7.2 (meaning probably trunk<\/a> at the time of writing) due to dependencies on the dynamic_type feature which was recently added.<\/p>\n

What’s supported right now:<\/h2>\n

nsCOMPtr<nsIFoo><\/h3>\n

If you print an nsCOMPtr, you’ll see one of two things:
\n[(nsIFoo*) 0x0]<\/code>
\nor
\n[(nsConcreteFoo*) 0x12345678]<\/code><\/p>\n

In addition, pretty-printers chain, so if there’s a pretty printer for nsConcreteFoo*, you’ll see that printed instead of just the pointer value. Furthermore, nsRefPtr and nsAutoPtr are also supported, and maybe nsWeakPtr (untested).<\/p>\n

nsCString\/nsString<\/h3>\n

It prints the string inline, up to the limit specified by gdb. This probably only works for ascii strings at the moment; the code is a bit of a mess.<\/p>\n

nsTArray\/InfallibleTArray<\/h3>\n

You’ll get output along the lines of [0x12345678, 0x12345678]<\/code> at the moment. Like the smart pointers, each printed element will be pretty-printed if possible.<\/p>\n

nsStandardURL*<\/h3>\n

You’ll see the spec printed. This works wonderfully when you’re looking at an object with nsCOMPtr<nsIURI> foo, where foo is actually pointing to an nsStandardURL object.<\/p>\n

Tagged reference counts<\/h3>\n

You know in cycle-collected objects when the refcount shows you mTagged = 0x8<\/code>? Yeah, not any more.<\/p>\n

PRPackedBool<\/h3>\n

I found the existing display of mBoolVal = 1 '\\001'<\/code> to be silly.<\/p>\n

What’s coming up?<\/h2>\n

I’ve got a list of things that still need fixing\/improving, and I’m open to suggestions\/patches.<\/p>\n