Mark one-parameter constructors as explicit & use override where possible

This commit marks (hopefully) ever one-parameter constructor as explicit.

It also uses override in (hopefully) all circumstances where a virtual
method is overridden.

There are a very few other minor changes - most of them were necessary
to get everything to compile (like one additional constructor). In one
case I changed an implicit operation to an explicit string conversion -
I think the automatically chosen conversion was much more convoluted.

This took longer than I want to admit but not as long as I feared :)

src/probabilistic/BloomFilter.h

@@ -19,7 +19,7 @@ public:
 	/**
 	 * Destructor.
 	 */
-	virtual ~BloomFilter();
+	~BloomFilter() override;
 
 	/**
 	 * Adds an element to the Bloom filter.
@@ -103,7 +103,7 @@ protected:
 	 *
 	 * @param hasher The hasher to use for this Bloom filter.
 	 */
-	BloomFilter(const Hasher* hasher);
+	explicit BloomFilter(const Hasher* hasher);
 
 	const Hasher* hasher;
 };
@@ -127,7 +127,7 @@ public:
 	/**
 	 * Destructor.
 	 */
-	~BasicBloomFilter();
+	~BasicBloomFilter() override;
 
 	/**
 	 * Computes the number of cells based on a given false positive rate
@@ -158,11 +158,11 @@ public:
 	static size_t K(size_t cells, size_t capacity);
 
 	// Overridden from BloomFilter.
-	virtual bool Empty() const override;
-	virtual void Clear() override;
-	virtual bool Merge(const BloomFilter* other) override;
-	virtual BasicBloomFilter* Clone() const override;
-	virtual string InternalState() const override;
+	bool Empty() const override;
+	void Clear() override;
+	bool Merge(const BloomFilter* other) override;
+	BasicBloomFilter* Clone() const override;
+	string InternalState() const override;
 
 protected:
 	DECLARE_SERIAL(BasicBloomFilter);
@@ -173,8 +173,8 @@ protected:
 	BasicBloomFilter();
 
 	// Overridden from BloomFilter.
-	virtual void Add(const HashKey* key) override;
-	virtual size_t Count(const HashKey* key) const override;
+	void Add(const HashKey* key) override;
+	size_t Count(const HashKey* key) const override;
 
 private:
 	BitVector* bits;
@@ -200,14 +200,14 @@ public:
 	/**
 	 * Destructor.
 	 */
-	~CountingBloomFilter();
+	~CountingBloomFilter() override;
 
 	// Overridden from BloomFilter.
-	virtual bool Empty() const override;
-	virtual void Clear() override;
-	virtual bool Merge(const BloomFilter* other) override;
-	virtual CountingBloomFilter* Clone() const override;
-	virtual string InternalState() const override;
+	bool Empty() const override;
+	void Clear() override;
+	bool Merge(const BloomFilter* other) override;
+	CountingBloomFilter* Clone() const override;
+	string InternalState() const override;
 
 protected:
 	DECLARE_SERIAL(CountingBloomFilter);
@@ -218,8 +218,8 @@ protected:
 	CountingBloomFilter();
 
 	// Overridden from BloomFilter.
-	virtual void Add(const HashKey* key) override;
-	virtual size_t Count(const HashKey* key) const override;
+	void Add(const HashKey* key) override;
+	size_t Count(const HashKey* key) const override;
 
 private:
 	CounterVector* cells;

src/probabilistic/CounterVector.h

@@ -26,7 +26,7 @@ public:
 	 *
 	 * @pre `cells > 0 && width > 0`
 	 */
-	CounterVector(size_t width, size_t cells = 1024);
+	explicit CounterVector(size_t width, size_t cells = 1024);
 
 	/**
 	 * Copy-constructs a counter vector.
@@ -38,7 +38,7 @@ public:
 	/**
 	 * Destructor.
 	 */
-	~CounterVector();
+	~CounterVector() override;
 
 	/**
 	 * Increments a given cell.

src/probabilistic/Hasher.h

@@ -43,7 +43,7 @@ public:
 	/**
 	 * Destructor.
 	 */
-	virtual ~Hasher() { }
+	~Hasher() override { }
 
 	/**
 	 * Computes hash values for an element.
@@ -138,7 +138,7 @@ public:
 	 *
 	 * @param arg_seed The seed to use for this instance.
 	 */
-	UHF(Hasher::seed_t arg_seed);
+	explicit UHF(Hasher::seed_t arg_seed);
 
 	template <typename T>
 	Hasher::digest operator()(const T& x) const
@@ -204,9 +204,9 @@ public:
 	DefaultHasher(size_t k, Hasher::seed_t seed);
 
 	// Overridden from Hasher.
-	virtual digest_vector Hash(const void* x, size_t n) const final;
-	virtual DefaultHasher* Clone() const final;
-	virtual bool Equals(const Hasher* other) const final;
+	digest_vector Hash(const void* x, size_t n) const final;
+	DefaultHasher* Clone() const final;
+	bool Equals(const Hasher* other) const final;
 
 	DECLARE_SERIAL(DefaultHasher);
 
@@ -232,9 +232,9 @@ public:
 	DoubleHasher(size_t k, Hasher::seed_t seed);
 
 	// Overridden from Hasher.
-	virtual digest_vector Hash(const void* x, size_t n) const final;
-	virtual DoubleHasher* Clone() const final;
-	virtual bool Equals(const Hasher* other) const final;
+	digest_vector Hash(const void* x, size_t n) const final;
+	DoubleHasher* Clone() const final;
+	bool Equals(const Hasher* other) const final;
 
 	DECLARE_SERIAL(DoubleHasher);
 

src/probabilistic/Topk.h

@@ -45,12 +45,12 @@ public:
 	 *
 	 * @return A newly initialized TopkVal
 	 */
-	TopkVal(uint64 size);
+	explicit TopkVal(uint64 size);
 
 	/**
 	 * Destructor.
 	 */
-	~TopkVal();
+	~TopkVal() override;
 
 	/**
 	 * Call this when a new value is encountered. Note that on the first