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--- intro_example:assertions [2025/05/17 12:02] – created rajit
+++ intro_example:assertions [2025/05/17 12:07] (current) – rajit
@@ Line 16: / Line 16: @@
 }
 </code>
+Passing in parameter 0 to this buffer would yield:
+<code act>
+buffer<0> x;
+</code>
+<code>
+--[ERROR]->
+In expanding buffer<0> (filename.act:XXXX)
+In expanding ::<Global>
+Error on or near line number XXXX.
+ id: b[0].L
+FATAL: Identifer conditionally created, but used when it does not exist
+</code>
+The definition, as written, does not support zero-length buffers. Rather than getting a message at expansion time that may not be as understandable to a user (especially of a pre-defined library), we can add an assertion to provide a more meaningful error message to a user of the templated buffer.
+<code act>
+template<pint N>
+defproc buffer(chan?(int) L; chan!(int) R)
+{
+    { N > 0 : "buffer size has to be at least 1" };
+    onebuf b[N];   // create one-place buffer elements
+    (i:N-1: b[i+1].L = b[i].R;)  // connect internal channels
+    b[0].L = L; // connect external input
+    b[N-1].R = R; // connect external output
+}
+</code>
+With this change, the error now looks like the following:
+<code>
+--[ERROR]->
+In expanding buffer<0> (filename.act:XXXX)
+In expanding ::<Global>
+Error on or near line number XXXX.
+*** Assertion failed ***
+ assertion: N>0
+   message: buffer size has to be at least 1
+</code>