Add 'explicit' to most single argument constructors

This prevents implicit conversions that we do not want, such
as having a FileFd* being converted to a debListParser.

Two cases are not yet handled because they require changes
in code using them:

1. The classes in hashes.h
2. The URI class - this one is used quite a lot

3 files changed, 4 insertions, 2 deletions

diff --git a/apt-private/private-cacheset.h b/apt-private/private-cacheset.h
index 3370bd03a..c52df36d7 100644
--- a/apt-private/private-cacheset.h
+++ b/apt-private/private-cacheset.h
@@ -18,6 +18,8 @@ class VerIteratorWithCaching
    const pkgCache::VerIterator iter;
    const pkgCache::DescFile * descFile;
 public:
+
+   // cppcheck-suppress noExplicitConstructor
    VerIteratorWithCaching(const pkgCache::VerIterator& iter) :
       iter(iter),
       descFile(iter->DescriptionList != 0
diff --git a/apt-private/private-json-hooks.cc b/apt-private/private-json-hooks.cc
index 65ff87924..3e0d8c93b 100644
--- a/apt-private/private-json-hooks.cc
+++ b/apt-private/private-json-hooks.cc
@@ -79,7 +79,7 @@ class APT_HIDDEN JsonWriter
    }
 
    public:
-   JsonWriter(std::ostream &os) : os(os) { old_locale = os.imbue(std::locale::classic()); }
+   explicit JsonWriter(std::ostream &os) : os(os) { old_locale = os.imbue(std::locale::classic()); }
    ~JsonWriter() { os.imbue(old_locale); }
    JsonWriter &beginArray()
    {
diff --git a/apt-private/private-sources.cc b/apt-private/private-sources.cc
index 713327f02..4cfb87938 100644
--- a/apt-private/private-sources.cc
+++ b/apt-private/private-sources.cc
@@ -31,7 +31,7 @@
 class APT_HIDDEN ScopedGetLock {
 public:
    int fd;
-   ScopedGetLock(std::string const &filename) : fd(GetLock(filename)) {}
+   explicit ScopedGetLock(std::string const &filename) : fd(GetLock(filename)) {}
    ~ScopedGetLock() { close(fd); }
 };
 bool EditSources(CommandLine &CmdL)