Replace many `const` variables with `constexpr`

constexpr is like const but (for variables) guarantees evaluation at
compile time (as opposed to runtime).

Likely this change will do nothing on its own (though it could, since
it gives the compiler more information). But it still has benefits.

It allows programmer to know that initialization is not expensive (it
was done at compile time), and reduces risk of a refactoring
regressing the compiletimeness.

Runtime initialization can be nonobvious in larger codebases. E.g.:
  struct S {
    static int foo();
  };
  const int bar = S::foo();  // Called and initialized at *runtime*.
  int S::foo() { return 10; }

With constexpr:
  struct S {
    static constexpr int foo();
  };
  constexpr int bar = S::foo();   // Error: used before definition.
  constexpr int S::foo() { return 10; }

Initializing at runtime is not just startup costs, but also can save
memory since it'll end up in a R/O section of a binary and therefore
doesn't need to be swapped out, but can be shared (in the mmap() sense
of the word).

2 files changed, 2 insertions, 2 deletions

diff --git a/gr-audio/lib/jack/jack_sink.h b/gr-audio/lib/jack/jack_sink.h
index 6c2ad24ba..60b501c9b 100644
--- a/gr-audio/lib/jack/jack_sink.h
+++ b/gr-audio/lib/jack/jack_sink.h
@@ -54,7 +54,7 @@ class jack_sink : public sink
     std::string d_device_name;
 
     jack_client_t* d_jack_client;
-    static const int MAX_PORTS = 10;
+    static constexpr int MAX_PORTS = 10;
     int d_portcount;
     jack_port_t* d_jack_output_port[MAX_PORTS];
     jack_ringbuffer_t* d_ringbuffer[MAX_PORTS];
diff --git a/gr-audio/lib/jack/jack_source.h b/gr-audio/lib/jack/jack_source.h
index e9a93a656..664a68d87 100644
--- a/gr-audio/lib/jack/jack_source.h
+++ b/gr-audio/lib/jack/jack_source.h
@@ -54,7 +54,7 @@ class jack_source : public source
     std::string d_device_name;
 
     jack_client_t* d_jack_client;
-    static const int MAX_PORTS = 10;
+    static constexpr int MAX_PORTS = 10;
     int d_portcount;
     jack_port_t* d_jack_input_port[MAX_PORTS];
     jack_ringbuffer_t* d_ringbuffer[MAX_PORTS];