Changes from Version 1 of StructTupleof

Author:

Cyborg16 (IP: 86.27.239.228)

Timestamp:

08/04/08 10:10:24 (16 years ago)

Comment:

--

StructTupleof

@@ +1 @@
+= Using .tupleof =
+
+The {{{.tupleof}}} struct property can be used to deal with structs generically.
+
+== Basic usage ==
+{{{
+#!d
+struct S { int a,b; }
+S s;
+s.tupleof[1] = 42;
+}}}
+
+== Iterating ==
+
+The index to .tupleof must be const, so you cannot, for instance, do:
+{{{
+#!d
+struct S { ... }
+S s;
+for (size_t i = 0; i < s.tupleof.length; ++i)
+    Stdout (s.tupleof[i]).newline;      // error: i is not const
+}}}
+
+But it is possible to use foreach:
+{{{
+#!d
+void printStruct(T) (T s)
+{
+    static assert (is(T == struct), "Only to be used with structs.");
+    
+    foreach (x,y; s.tupleof)
+        Stdout.format ("Element: {}:{}", x,y).newline;
+}
+It doesn't seem to be possible to set the elements of a struct using foreach, however (correct me if I'm wrong; I couldn't make it work).
+}}}
+
+== Setting the elements ==
+The following is a function I wrote to set all elements of a struct from a static array, to get around the difficulty of setting elements while iterating over the tuple. (It could easily be converted to read from a dynamic array.)
+{{{
+#!d
+// only used for error reporting:
+// Int-to-string converter, which may not be efficient but will run at compile time.
+static char[] int2str (uint i) {
+    char[] ret;
+    const digits = "0123456789";
+    if (i == 0) ret = "0";
+    else for (; i > 0; i /= 10) ret = digits[i%10] ~ ret;
+    return ret;
+}
+
+/** Set a struct's elements from an array, where all elements in the struct have the same type (or
+ * can be implicitly converted to from the same type).
+ *
+ * ---
+ * struct S { int a,b,c; }
+ * S s;
+ * int[3] v = [1,2,3];
+ * setStruct (s,v);
+ * ---
+ *
+ * It works fine. I'm not sure about the efficiency (do the recursive calls get inlined?).
+ */
+void setStruct(S, T, size_t N, size_t i = 0) (ref S s, T[N] src) {
+    static assert (is(S == struct), "Only to be used with structs.");
+    static assert (N == S.tupleof.length, "src.length == "~int2str(N)~"; should equal "~int2str(S.tupleof.length));
+    static if (i < N) {
+        s.tupleof[i] = src[i];
+        setStruct!(S, T, N, i+1) (s, src);
+    }
+}
+}}}
+
+== Example ==
+Using the above functions, this can be done:
+{{{
+#!d
+struct S2
+{
+    //char[] first, second, third;
+    uint a;
+    byte b;
+    ulong c;
+    float d;
+}
+
+void main() {
+    S2 v;
+    //char[][3] vals = ["One"[], "Two", "Three"];
+    long[4] vals = [-1L,-100,10000000000, 2];
+    setStruct(v, vals);
+    printStruct(v);
+}
+}}}
+
+
+= Source =
+|| Posted by || Cyborg16 ||
+|| Date ||  August 4, 2008 ||