WIP initial design

src/libutil/hash.cc

@@ -132,10 +132,13 @@ std::string Hash::to_string(Base base, bool includeType) const
     return s;
 }
 
-Hash::Hash(std::string_view s, HashType type) : Hash(s, std::optional { type }) { }
-Hash::Hash(std::string_view s) : Hash(s, std::optional<HashType>{}) { }
+Hash fromSRI(std::string_view original) {
 
-Hash::Hash(std::string_view original, std::optional<HashType> optType)
+}
+
+Hash::Hash(std::string_view s) : Hash(s, std::nullopt) { }
+
+static HashType newFunction(std::string_view & rest, std::optional<HashType> optType)
 {
     auto rest = original;
 
@@ -161,13 +164,17 @@ Hash::Hash(std::string_view original, std::optional<HashType> optType)
     if (!optParsedType && !optType) {
         throw BadHash("hash '%s' does not include a type, nor is the type otherwise known from context.", rest);
     } else {
-        this->type = optParsedType ? *optParsedType : *optType;
         if (optParsedType && optType && *optParsedType != *optType)
             throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
+        return optParsedType ? *optParsedType : *optType;
     }
+}
 
-    init();
+// mutates the string_view
+Hash::Hash(std::string_view original, std::optional<HashType> optType)
+    : Hash(original, newFunction(original, optType))
 
+Hash::Hash(std::string_view original, HashType type) : Hash(type) {
     if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {

src/libutil/hash.hh

@@ -40,13 +40,16 @@ struct Hash
        is not present, then the hash type must be specified in the
        string. */
     Hash(std::string_view s, std::optional<HashType> type);
-    // type must be provided
-    Hash(std::string_view s, HashType type);
     // hash type must be part of string
     Hash(std::string_view s);
 
+private:
+    // type must be provided, s must not include <type> prefix
+    Hash(std::string_view s, HashType type);
+
     void init();
 
+public:
     /* Check whether a hash is set. */
     operator bool () const { return (bool) type; }
 

src/libutil/parser.hh

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <optional>
+#include <string_view>
 
 namespace nix {
 
@@ -8,9 +9,7 @@ namespace nix {
 // separator, and modify the string argument to contain only the part after the
 // separator. Otherwise, wer return `std::nullopt`, and we leave the argument
 // string alone.
-std::optional<std::string_view> splitPrefix(std::string_view & string, char separator);
-
-std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
+static inline std::optional<std::string_view> splitPrefix(std::string_view & string, char separator) {
     auto sepInstance = string.find(separator);
 
     if (sepInstance != std::string_view::npos) {