/// <summary>Returns the next token without advancing the lexer.</summary>
/// <returns>The next token.</returns>
internal ExpressionToken PeekNextToken()
{
DebugUtils.CheckNoExternalCallers();
int savedTextPos = this.textPos;
char savedChar = this.ch;
ExpressionToken savedToken = this.token;
this.NextToken();
ExpressionToken result = this.token;
this.textPos = savedTextPos;
this.ch = savedChar;
this.token = savedToken;
return result;
}
/// <summary>Attempts to parse key values from the specified text.</summary>
/// <param name='text'>Text to parse (not null).</param>
/// <returns>
/// Enumeration of key values or null if there was a syntax error.
/// </returns>
/// <remarks>
/// The returned instance contains only string values.
/// </remarks>
private static IEnumerable <NamedValue> ParseKeyValuesFromUri(string text)
{
Debug.Assert(text != null, "text != null");
//// This is a modified copy of KeyInstance.TryParseFromUri
ExpressionLexer lexer = new ExpressionLexer(text);
ExpressionToken currentToken = lexer.CurrentToken;
if (currentToken.Kind == ExpressionTokenKind.End)
{
return(EmptyKeyValues);
}
List <NamedValue> keyValuesList = new List <NamedValue>();
do
{
if (currentToken.Kind == ExpressionTokenKind.Identifier)
{
// Name-value pair.
string identifier = lexer.CurrentToken.GetIdentifier();
lexer.NextToken();
if (lexer.CurrentToken.Kind != ExpressionTokenKind.Equal)
{
return(null);
}
lexer.NextToken();
if (!lexer.CurrentToken.IsKeyValueToken)
{
return(null);
}
keyValuesList.Add(new NamedValue()
{
Name = identifier, Value = ParseKeyValueLiteral(lexer)
});
}
else if (currentToken.IsKeyValueToken)
{
// Unnamed value.
keyValuesList.Add(new NamedValue()
{
Value = ParseKeyValueLiteral(lexer)
});
}
else
{
return(null);
}
// Read the next token. We should be at the end, or find
// we have a comma followed by something.
currentToken = lexer.NextToken();
if (currentToken.Kind == ExpressionTokenKind.Comma)
{
currentToken = lexer.NextToken();
if (currentToken.Kind == ExpressionTokenKind.End)
{
// Trailing comma.
return(null);
}
}
}while (currentToken.Kind != ExpressionTokenKind.End);
return(keyValuesList);
}