We initially did not have this impl because the first revision of the Sink
trait was much more complicated. In particular, each method was
parameterized over a Matcher. But not every Sink impl actually needs a
Matcher, and it is just as easy to borrow a Matcher explicitly, so the
added parameterization wasn't holding its own.
This does permit Sink implementations to be used as trait objects. One
key use case here is to reduce compile times, since there is quite a bit
of code inside grep-searcher that is parameterized on Sink. Unfortunately,
that code is *also* parameterized on Matcher, and the various printers in
grep-printer are also parameterized on Matcher, which means Sink trait
objects are necessary but no sufficient for a major reduction in compile
times. Unfortunately, the path to making Matcher object safe isn't quite
clear. Extension traits maybe? There's also stuff in the Serde ecosystem
that might help, but the type shenanigans can get pretty gnarly.
libripgrep is not any one library, but rather, a collection of libraries
that roughly separate the following key distinct phases in a grep
implementation:
1. Pattern matching (e.g., by a regex engine).
2. Searching a file using a pattern matcher.
3. Printing results.
Ultimately, both (1) and (3) are defined by de-coupled interfaces, of
which there may be multiple implementations. Namely, (1) is satisfied by
the `Matcher` trait in the `grep-matcher` crate and (3) is satisfied by
the `Sink` trait in the `grep2` crate. The searcher (2) ties everything
together and finds results using a matcher and reports those results
using a `Sink` implementation.
Closes#162
