From b798efb829415eb47a532e9479523afdff74eca7 Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Tue, 30 Jun 2020 14:10:30 -0400
Subject: [PATCH] WIP initial design

---
 src/libutil/hash.cc   | 17 ++++++++++++-----
 src/libutil/hash.hh   |  7 +++++--
 src/libutil/parser.hh |  5 ++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 26ab5a110..36de293bb 100644
--- a/src/libutil/hash.cc
+++ b/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) {
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index a55295912..42bd585a2 100644
--- a/src/libutil/hash.hh
+++ b/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; }
 
diff --git a/src/libutil/parser.hh b/src/libutil/parser.hh
index 64689e283..d3bfafe75 100644
--- a/src/libutil/parser.hh
+++ b/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) {