How does portaudio custom datatypes work?

I am working with the portaudio lib for c and c++ on a small project and i came across their custom datatypes they use as sample types and i have no clue how the definition of the types work.

I have tried googling the code but no results show what i have experienced.

When they define the datatype they use the the #define preprocessor function to define it like so.

typedef unsigned long PaSampleFormat

#define paFloat32 ((PaSampleFormat) 0x00000001)

Then my question is how does the ((PaSampleFormat) 0x00000001) part work when you use it as a datatype.