Improve collection-to-str conversions

stdlib/internal/types/collections/dict.codon

@@ -140,23 +140,24 @@ class Dict:
         return {k.__deepcopy__(): v.__deepcopy__() for k, v in self.items()}
 
     def __repr__(self) -> str:
+        from internal.types.strbuf import strbuf
         n = self.__len__()
         if n == 0:
             return "{}"
         else:
-            lst = []
-            lst.append("{")
+            buf = strbuf()
+            buf.append("{")
             first = True
             for k, v in self.items():
                 if not first:
-                    lst.append(", ")
+                    buf.append(", ")
                 else:
                     first = False
-                lst.append(k.__repr__())
-                lst.append(": ")
-                lst.append(v.__repr__())
-            lst.append("}")
-            return str.cat(lst)
+                buf.append(k.__repr__())
+                buf.append(": ")
+                buf.append(v.__repr__())
+            buf.append("}")
+            return buf.__str__()
 
     # Helper methods
 

stdlib/internal/types/collections/list.codon

@@ -267,16 +267,19 @@ class List:
         return self
 
     def __repr__(self) -> str:
+        from internal.types.strbuf import strbuf
         n = self.__len__()
         if n == 0:
             return "[]"
         else:
-            y = ["[", self[0].__repr__()]
+            buf = strbuf()
+            buf.append("[")
+            buf.append(self[0].__repr__())
             for i in range(1, n):
-                y.append(", ")
-                y.append(self[i].__repr__())
-            y.append("]")
-            return str.cat(y)
+                buf.append(", ")
+                buf.append(self[i].__repr__())
+            buf.append("]")
+            return buf.__str__()
 
     # Helper functions
 

stdlib/internal/types/collections/set.codon

@@ -130,21 +130,22 @@ class Set:
         return {s.__deepcopy__() for s in self}
 
     def __repr__(self) -> str:
+        from internal.types.strbuf import strbuf
         n = self.__len__()
         if n == 0:
             return "{}"
         else:
-            lst = []
-            lst.append("{")
+            buf = strbuf()
+            buf.append("{")
             first = True
             for k in self:
                 if not first:
-                    lst.append(", ")
+                    buf.append(", ")
                 else:
                     first = False
-                lst.append(k.__repr__())
-            lst.append("}")
-            return str.cat(lst)
+                buf.append(k.__repr__())
+            buf.append("}")
+            return buf.__str__()
 
     # Helper methods
 

stdlib/internal/types/strbuf.codon

@@ -0,0 +1,27 @@
+# (c) 2022 Exaloop Inc. All rights reserved.
+
+class strbuf:
+    data: Ptr[byte]
+    n: int
+    m: int
+
+    def __init__(self, capacity: int = 16):
+        self.data = Ptr[byte](capacity)
+        self.n = 0
+        self.m = capacity
+
+    def append(self, s: str):
+        from internal.gc import realloc
+        adding = s.__len__()
+        needed = self.n + adding
+        if needed > self.m:
+            m = self.m
+            while m < needed:
+                m *= 2
+            self.data = realloc(self.data, m, self.m)
+            self.m = m
+        str.memcpy(self.data + self.n, s.ptr, adding)
+        self.n = needed
+
+    def __str__(self):
+        return str(self.data, self.n)

test/core/containers.codon

@@ -304,6 +304,9 @@ def test_extendedslicing():
     a = list(range(10))
     a[::2] = (0, 1, 2, 3, 4)
     assert a == [0, 1, 1, 3, 2, 5, 3, 7, 4, 9]
+
+    assert repr(['x', 'y', 'z']) == "['x', 'y', 'z']"
+    assert repr(List[int]()) == '[]'
 test_extendedslicing()
 
 @test
@@ -378,6 +381,9 @@ def test_set():
         assert False
     except ValueError:
         pass
+
+    assert repr({(1,2)}) == '{(1, 2)}'
+    assert repr(Set[int]()) == '{}'
 test_set()
 
 @test
@@ -417,6 +423,9 @@ def test_dict():
     assert d3 | d4 == {1: 5, 42: 42, 2: 9}
     d3 |= d4
     assert d3 == {1: 5, 42: 42, 2: 9}
+
+    assert repr({1: ['x']}) == "{1: ['x']}"
+    assert repr(Dict[int,int]()) == '{}'
 test_dict()
 
 @test