@system blocks and safer @trusted (ST) functions

[Joseph Rushton Wakeling]

On Wednesday, 28 July 2021 at 17:25:18 UTC, claptrap wrote:
> Do you have ideas on how to stop unsafe blocks accessing the 
> variables from the surrounding scope? Is that even a goal for 
> the DIP?

I'm not sure it necessarily is.  Consider the following example 
(using the proposed @trusted-with- at system-blocks syntax):


```D
/// Writes something into the provided buffer, e.g. filling the
/// buffer with random bytes
extern(C) void writeIntoCBuffer (int* ptr, size_t len) @system;


void writeIntoDBuffer (ref int[] buf) @trusted
{
     @system { writeIntoCBuffer(buf.ptr, buf.length); }
}
```

That seems like a reasonable use-case for a @trusted wrapper of 
an underlying @system function, but if the @system block was 
forbidden from accessing variables from the surrounding scope, it 
wouldn't be possible.

Does that make sense, or have I misunderstood what you had in 
mind?