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digitalmars.D.debugger - Hopper for low level D debug

Hopper

https://www.hopperapp.com/

Is not so bad for low level debugging (à la IDA).
The symbols are not demangled however.
I've recently used it to check a call to SDL in a D app:

https://imgur.com/a/vsJiu

The integrated debugger is actually using GDB (at least on linux).
Jan 23 2018