Clarify initialization of containers

docs/pages/libraries.md

@@ -1614,6 +1614,8 @@ are agnostic to the input container type.
 
 Spans are also known as "fat pointer" or "slice" in some other languages.
 
+Remarks: A span initialized from a list of unnamed fields points to an array of the list elements.
+
 ### spanT
 
 ```nelua
@@ -2877,6 +2879,8 @@ A vector has the following semantics:
 otherwise the behavior is undefined, in case this is needed then try the `sequence` library.
 * Any failure when growing a vector raises an error.
 
+Remarks: A vector initialized from a list of unnamed fields is filled with the list elements.
+
 ### vectorT
 
 ```nelua
@@ -3069,6 +3073,8 @@ thus the list itself is passed by reference by default (like lua tables again).
 A sequence is typically used as a more efficient table that
 can hold only sequences of a fixed value type.
 
+Remarks: A sequence initialized from a list of unnamed fields is filled with the list elements.
+
 ### sequenceT
 
 ```nelua

lib/sequence.nelua

@@ -10,6 +10,8 @@ thus the list itself is passed by reference by default (like lua tables again).
 
 A sequence is typically used as a more efficient table that
 can hold only sequences of a fixed value type.
+
+Remarks: A sequence initialized from a list of unnamed fields is filled with the list elements.
 ]]
 
 require 'memory'
@@ -56,7 +58,9 @@ require 'span'
     end
     return false, string.format("no viable conversion from '%s' to '%s'", x.type, sequenceT)
   end, function(node)
-    return node.tag == 'InitList' and types.ArrayType(T, #node)
+    if node.is_InitList and #node > 0 and not node:find_child_with_field('is_Pair') then
+      return node.tag == 'InitList' and types.ArrayType(T, #node)
+    end
   end)]#
 
   --[[

lib/span.nelua

@@ -9,6 +9,8 @@ Spans are especially useful for making functions with arguments that
 are agnostic to the input container type.
 
 Spans are also known as "fat pointer" or "slice" in some other languages.
+
+Remarks: A span initialized from a list of unnamed fields points to an array of the list elements.
 ]]
 
 ## local function make_spanT(T)

lib/vector.nelua

@@ -6,6 +6,8 @@ A vector has the following semantics:
 * It should never be passed by value while being modified,
 otherwise the behavior is undefined, in case this is needed then try the `sequence` library.
 * Any failure when growing a vector raises an error.
+
+Remarks: A vector initialized from a list of unnamed fields is filled with the list elements.
 ]]
 
 require 'memory'
@@ -46,7 +48,9 @@ require 'span'
     end
     return false, string.format("no viable conversion from '%s' to '%s'", x.type, vectorT)
   end, function(node)
-    return node.tag == 'InitList' and types.ArrayType(T, #node)
+    if node.is_InitList and #node > 0 and not node:find_child_with_field('is_Pair') then
+      return node.tag == 'InitList' and types.ArrayType(T, #node)
+    end
   end)]#
 
   --[[

tests/sequence_test.nelua

@@ -11,7 +11,7 @@ end
 
 do -- braces initializer
   local seq: sequence(integer) = {}
-  assert(#seq == 0 and seq.impl ~= nilptr)
+  assert(#seq == 0 and seq.impl == nilptr)
   seq:destroy()
   seq = {1,2,3}
   assert(#seq == 3 and seq[0] == 0 and seq[1] == 1 and seq[2] == 2 and seq[3] == 3)