Support for literals in INSERT and UPDATE and comparisons

The 'value' interface represents a CQL value for use in a comparison,
update, or intitialization operation. A consistent interface for this
allows us to easily support specifying default-named, custom-named,
literal, and evaluated-function values in all these contexts.

Parameters to Func should probably also be values to support full
composition, but that would be a breaking change because Func's
properties are exposed.

The value interface could itself be exposed if we wanted to allow
clients to pass their own values to SetValue, etc, but for now it is a
package-internal abstraction.

BLA

qb/insert.go

@@ -11,10 +11,16 @@ import (
 	"bytes"
 )
 
+// initializer specifies an value for a column in an insert operation.
+type initializer struct {
+	column string
+	value  value
+}
+
 // InsertBuilder builds CQL INSERT statements.
 type InsertBuilder struct {
 	table   string
-	columns columns
+	columns []initializer
 	unique  bool
 	using   using
 }
@@ -37,12 +43,21 @@ func (b *InsertBuilder) ToCql() (stmt string, names []string) {
 	cql.WriteByte(' ')
 
 	cql.WriteByte('(')
-	b.columns.writeCql(&cql)
-	names = append(names, b.columns...)
+	for i, c := range b.columns {
+		cql.WriteString(c.column)
+		if i < len(b.columns)-1 {
+			cql.WriteByte(',')
+		}
+	}
 	cql.WriteString(") ")
 
 	cql.WriteString("VALUES (")
-	placeholders(&cql, len(b.columns))
+	for i, c := range b.columns {
+		names = append(names, c.value.writeCql(&cql)...)
+		if i < len(b.columns)-1 {
+			cql.WriteByte(',')
+		}
+	}
 	cql.WriteString(") ")
 
 	if b.unique {
@@ -62,7 +77,39 @@ func (b *InsertBuilder) Into(table string) *InsertBuilder {
 
 // Columns adds insert columns to the query.
 func (b *InsertBuilder) Columns(columns ...string) *InsertBuilder {
-	b.columns = append(b.columns, columns...)
+	for _, c := range columns {
+		b.columns = append(b.columns, initializer{
+			column: c,
+			value:  param(c),
+		})
+	}
+	return b
+}
+
+// NamedColumn adds an insert column with a custom parameter name.
+func (b *InsertBuilder) NamedColumn(column, name string) *InsertBuilder {
+	b.columns = append(b.columns, initializer{
+		column: column,
+		value:  param(name),
+	})
+	return b
+}
+
+// LitColumn adds an insert column with a literal value to the query.
+func (b *InsertBuilder) LitColumn(column, literal string) *InsertBuilder {
+	b.columns = append(b.columns, initializer{
+		column: column,
+		value:  lit(literal),
+	})
+	return b
+}
+
+// FuncColumn adds an insert column initialized by evaluating a CQL function.
+func (b *InsertBuilder) FuncColumn(column string, fn *Func) *InsertBuilder {
+	b.columns = append(b.columns, initializer{
+		column: column,
+		value:  fn,
+	})
 	return b
 }