On Tuesday, 15 September 2015 at 17:45:45 UTC, Freddy wrote:
Would it be worth implementing some kind of typestate into the
language?
By typestate I mean a modifiable enum.
For example:
---
enum FState
{
none,
read,
write
}
struct File
{
//maybe another keyword other than enum
enum state = FState.none;
void openRead(string name)
{
//evalutaed in a way similar to static if
state = FState.read;
//...
}
void openWrite(string name)
{
state = FState.write;
//...
}
ubyte[] read(size_t) if (state == FState.read)
{
//...
}
void write(ubyte[]) if (state == FState.write)
{
//...
}
}
unittest
{
File f;
static assert(f.state == FState.none);
f.openRead("a.txt");
static assert(f.state == FState.read);
auto data = f.read(10);
}
---
We could use this "typestate" to implement:
Rust style memory management in a library
Safer Files (as shown)
Possibly other ideas
Thoughts?
This won't work in D. Everything that's static is common to each
instance.
What's possible however is to use an immutable FState that's set
in the ctor.
---
struct File
{
immutable FState state,
this(string fname, FState st){state = st}
}
---
Than you're sure that your file state can't be changed by error.
Otherwise just hide the state to set it as a private variable...
