std/collections: add RingBuffer.popc()

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

lib/std/collections/ringbuffer.c3

@@ -37,6 +37,21 @@ fn Type RingBuffer.getc(&self, usz index)
 	return self.buf[index - avail];
 }
 
+fn Type! RingBuffer.popc(&self)
+{
+	switch
+	{
+		case self.written == 0:
+			return SearchResult.MISSING?;
+		case self.written < SIZE:
+			self.written--;
+			return self.buf[self.written];
+		default:
+			self.head = (self.head - 1) % SIZE;
+			return self.buf[self.head];
+	}
+}
+
 fn usz RingBuffer.get(&self, usz index, Type[] buffer)
 {
 	index %= SIZE;

test/unit/stdlib/collections/ringbuffer.c3

@@ -4,7 +4,7 @@ import std::io;
 
 def Buffer = RingBuffer(<char, 4>);
 
-fn void putc_getc()
+fn void! putc_getc()
 {
 	Buffer rb;
 	rb.init();
@@ -23,4 +23,7 @@ fn void putc_getc()
 	assert(rb.getc(1) == 3);
 	assert(rb.getc(2) == 4);
 	assert(rb.getc(3) == 5);
+
+	char c = rb.popc()!;
+	assert(c == 5);
 }