Replace function pointers for base encode/decode with virtual methods

Author: Ericson2314

src/libutil/base-n.cc

@@ -177,28 +177,62 @@ std::string base64::decode(std::string_view s)
     return res;
 }
 
-decltype(base16::encode) * encodeForBase(Base base)
+namespace {
+
+struct Base16Encoding final : BaseEncoding
 {
-    switch (base) {
-    case Base::Base16:
-        return base16::encode;
-    case Base::Nix32:
-        return BaseNix32::encode;
-    case Base::Base64:
-        return base64::encode;
+    std::string encode(std::span<const std::byte> data) const override
+    {
+        return base16::encode(data);
     }
-    unreachable();
-}
 
-decltype(base16::decode) * decodeForBase(Base base)
+    std::string decode(std::string_view s) const override
+    {
+        return base16::decode(s);
+    }
+};
+
+struct Nix32Encoding final : BaseEncoding
+{
+    std::string encode(std::span<const std::byte> data) const override
+    {
+        return BaseNix32::encode(data);
+    }
+
+    std::string decode(std::string_view s) const override
+    {
+        return BaseNix32::decode(s);
+    }
+};
+
+struct Base64Encoding final : BaseEncoding
+{
+    std::string encode(std::span<const std::byte> data) const override
+    {
+        return base64::encode(data);
+    }
+
+    std::string decode(std::string_view s) const override
+    {
+        return base64::decode(s);
+    }
+};
+
+const Base16Encoding base16Encoding;
+const Nix32Encoding nix32Encoding;
+const Base64Encoding base64Encoding;
+
+} // anonymous namespace
+
+const BaseEncoding & getBaseEncoding(Base base)
 {
     switch (base) {
     case Base::Base16:
-        return base16::decode;
+        return base16Encoding;
     case Base::Nix32:
-        return BaseNix32::decode;
+        return nix32Encoding;
     case Base::Base64:
-        return base64::decode;
+        return base64Encoding;
     }
     unreachable();
 }

src/libutil/hash.cc

@@ -91,7 +91,7 @@ std::string Hash::to_string(HashFormat hashFormat, bool includeAlgo) const
         hashFormat.raw);
     const auto bytes = std::as_bytes(std::span<const uint8_t>{&hash[0], hashSize});
     assert(hashSize);
-    s += encodeForBase(hashFormat.toBase())(bytes);
+    s += getBaseEncoding(hashFormat.toBase()).encode(bytes);
     return s;
 }
 
@@ -125,7 +125,7 @@ static Hash parseLowLevel(
     Hash res{algo, xpSettings};
     std::string d;
     try {
-        d = decodeForBase(format.toBase())(rest);
+        d = getBaseEncoding(format.toBase()).decode(rest);
     } catch (Error & e) {
         e.addTrace({}, "While decoding hash '%s'", rest);
     }

src/libutil/include/nix/util/base-n.hh

@@ -101,13 +101,26 @@ std::string decode(std::string_view s);
 } // namespace base64
 
 /**
- * Get the encoding function for the given base encoding.
+ * Abstract interface for base-N encoding/decoding operations.
  */
-decltype(base16::encode) * encodeForBase(Base base);
+struct BaseEncoding
+{
+    virtual ~BaseEncoding() = default;
+
+    /**
+     * Encode arbitrary bytes to a string.
+     */
+    virtual std::string encode(std::span<const std::byte> data) const = 0;
+
+    /**
+     * Decode a string to bytes.
+     */
+    virtual std::string decode(std::string_view s) const = 0;
+};
 
 /**
- * Get the decoding function for the given base encoding.
+ * Get the encoding/decoding functions for the given base encoding.
  */
-decltype(base16::decode) * decodeForBase(Base base);
+const BaseEncoding & getBaseEncoding(Base base);
 
 } // namespace nix