diff --git a/pkgs/ruby/ext/default/dynarg.c b/pkgs/ruby/ext/default/dynarg.c
new file mode 100644
index 0000000..d45b72c
--- /dev/null
+++ b/pkgs/ruby/ext/default/dynarg.c
@@ -0,0 +1,45 @@
+#include "dynarg.h"
+
+struct DynArg DynArg_create()
+{
+    struct DynArg dynarg;
+    DynArg_init(&dynarg);
+    return dynarg;
+}
+
+void DynArg_init(struct DynArg *const dynarg)
+{
+    dynarg->use_dbl = false;
+    dynarg->dbl = 0.0;
+    dynarg->arg.str = "";
+}
+
+void DynArg_use_char(struct DynArg *const dynarg, const char chr)
+{
+    dynarg->use_dbl = false;
+    dynarg->arg.chr = chr;
+}
+
+void DynArg_use_double(struct DynArg *const dynarg, const double dbl)
+{
+    dynarg->use_dbl = true;
+    dynarg->dbl = dbl;
+}
+
+void DynArg_use_long_long(struct DynArg *const dynarg, const long long ll)
+{
+    dynarg->use_dbl = false;
+    dynarg->arg.ll = ll;
+}
+
+void DynArg_use_str(struct DynArg *const dynarg, const char *const str)
+{
+    dynarg->use_dbl = false;
+    dynarg->arg.str = str;
+}
+
+void DynArg_use_unsigned_long_long(struct DynArg *const dynarg, const unsigned long long ull)
+{
+    dynarg->use_dbl = false;
+    dynarg->arg.ull = ull;
+}
diff --git a/pkgs/ruby/ext/default/dynarg.h b/pkgs/ruby/ext/default/dynarg.h
new file mode 100644
index 0000000..e6f70c0
--- /dev/null
+++ b/pkgs/ruby/ext/default/dynarg.h
@@ -0,0 +1,35 @@
+#ifndef INCLUDED_DYNARG
+#define INCLUDED_DYNARG
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdbool.h>
+
+struct DynArg {
+    bool use_dbl;
+    double dbl;
+    // TODO: check if this will work on different endianness.
+    union {
+        char chr;
+        long long ll;
+        const char *str;
+        unsigned long long ull;
+    } __attribute__((packed)) arg;
+};
+
+struct DynArg DynArg_create();
+void DynArg_init(struct DynArg *dynarg);
+
+void DynArg_use_char(struct DynArg *dynarg, char chr);
+void DynArg_use_double(struct DynArg *dynarg, double dbl);
+void DynArg_use_long_long(struct DynArg *dynarg, long long ll);
+void DynArg_use_str(struct DynArg *dynarg, const char *str);
+void DynArg_use_unsigned_long_long(struct DynArg *dynarg, unsigned long long ull);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/pkgs/ruby/ext/default/printf.c b/pkgs/ruby/ext/default/printf.c
index 5a893bc..acf4c95 100644
--- a/pkgs/ruby/ext/default/printf.c
+++ b/pkgs/ruby/ext/default/printf.c
@@ -1,6 +1,8 @@
 #include <kernaux.h>
 #include <ruby.h>
 
+#include "dynarg.h"
+
 #ifdef HAVE_KERNAUX_SNPRINTF
 
 static VALUE rb_KernAux_snprintf1(int argc, const VALUE *argv, VALUE self);
@@ -89,37 +91,29 @@ VALUE rb_KernAux_snprintf1(
     int width = 0;
     if (has_width && argc > 2) width = NUM2INT(argv_rb[2]);
 
-    bool use_dbl = false;
-    double dbl;
-    union {
-        const char *str;
-        long long ll;
-        unsigned long long ull;
-        char chr;
-    } __attribute__((packed)) arg = { .str = "" };
+    struct DynArg dynarg = DynArg_create();
 
     if (argc == (has_width ? 4 : 3)) {
         VALUE arg_rb = argv_rb[has_width ? 3 : 2];
 
         if (c == 'd' || c == 'i') {
             RB_INTEGER_TYPE_P(arg_rb);
-            arg.ll = NUM2LL(arg_rb);
+            DynArg_use_long_long(&dynarg, NUM2LL(arg_rb));
         } else if (c == 'u' || c == 'x' || c == 'X' || c == 'o' || c == 'b') {
             RB_INTEGER_TYPE_P(arg_rb);
-            arg.ull = NUM2ULL(arg_rb);
+            DynArg_use_unsigned_long_long(&dynarg, NUM2ULL(arg_rb));
         } else if (c == 'f' || c == 'F' ||
                    c == 'e' || c == 'E' ||
                    c == 'g' || c == 'G')
         {
             RB_FLOAT_TYPE_P(arg_rb);
-            use_dbl = true;
-            dbl = NUM2DBL(arg_rb);
+            DynArg_use_double(&dynarg, NUM2DBL(arg_rb));
         } else if (c == 'c') {
             Check_Type(arg_rb, T_STRING);
-            arg.chr = *StringValuePtr(arg_rb);
+            DynArg_use_char(&dynarg, *StringValuePtr(arg_rb));
         } else if (c == 's') {
             Check_Type(arg_rb, T_STRING);
-            arg.str = StringValueCStr(arg_rb);
+            DynArg_use_str(&dynarg, StringValueCStr(arg_rb));
         }
     }
 
@@ -128,13 +122,13 @@ VALUE rb_KernAux_snprintf1(
 
     int slen;
     if (has_width) {
-        slen = use_dbl
-            ? kernaux_snprintf(str, size, format, width, dbl)
-            : kernaux_snprintf(str, size, format, width, arg);
+        slen = dynarg.use_dbl
+            ? kernaux_snprintf(str, size, format, width, dynarg.dbl)
+            : kernaux_snprintf(str, size, format, width, dynarg.arg);
     } else {
-        slen = use_dbl
-            ? kernaux_snprintf(str, size, format, dbl)
-            : kernaux_snprintf(str, size, format, arg);
+        slen = dynarg.use_dbl
+            ? kernaux_snprintf(str, size, format, dynarg.dbl)
+            : kernaux_snprintf(str, size, format, dynarg.arg);
     }
 
     const VALUE output_rb =