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## Classification of await expressions
The expression await
At runtime, the expression await · An awaiter · A bool · If o If o If o Evaluation is then suspended, and control is returned to the current caller of the async function. · Either immediately after (if An awaiter’s implementation of the interface methods INotifyCompletion.OnCompleted and ICriticalNotifyCompletion.UnsafeOnCompleted should cause the delegate
The *, /, %, +, and – operators are called the arithmetic operators. multiplicative-expression: additive-expression: If an operand of an arithmetic operator has the compile-time type dynamic, then the expression is dynamically bound (§7.2.2). In this case the compile-time type of the expression is dynamic, and the resolution described below will take place at run-time using the run-time type of those operands that have the compile-time type dynamic.
For an operation of the form x * y, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. The predefined multiplication operators are listed below. The operators all compute the product of x and y. · Integer multiplication: int operator *(int x, int y); In a checked context, if the product is outside the range of the result type, a System.OverflowException is thrown. In an unchecked context, overflows are not reported and any significant high-order bits outside the range of the result type are discarded. · Floating-point multiplication: float operator *(float x, float y); The product is computed according to the rules of IEEE 754 arithmetic. The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaN’s. In the table, x and y are positive finite values. z is the result of x * y. If the result is too large for the destination type, z is infinity. If the result is too small for the destination type, z is zero.
· Decimal multiplication: decimal operator *(decimal x, decimal y); If the resulting value is too large to represent in the decimal format, a System.OverflowException is thrown. If the result value is too small to represent in the decimal format, the result is zero. The scale of the result, before any rounding, is the sum of the scales of the two operands. Decimal multiplication is equivalent to using the multiplication operator of type System.Decimal.
For an operation of the form x / y, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. The predefined division operators are listed below. The operators all compute the quotient of x and y. · Integer division: int operator /(int x, int y); If the value of the right operand is zero, a System.DivideByZeroException is thrown. The division rounds the result towards zero. Thus the absolute value of the result is the largest possible integer that is less than or equal to the absolute value of the quotient of the two operands. The result is zero or positive when the two operands have the same sign and zero or negative when the two operands have opposite signs. If the left operand is the smallest representable int or long value and the right operand is –1, an overflow occurs. In a checked context, this causes a System.ArithmeticException (or a subclass thereof) to be thrown. In an unchecked context, it is implementation-defined as to whether a System.ArithmeticException (or a subclass thereof) is thrown or the overflow goes unreported with the resulting value being that of the left operand. · Floating-point division: float operator /(float x, float y); The quotient is computed according to the rules of IEEE 754 arithmetic. The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaN’s. In the table, x and y are positive finite values. z is the result of x / y. If the result is too large for the destination type, z is infinity. If the result is too small for the destination type, z is zero.
· Decimal division: decimal operator /(decimal x, decimal y); If the value of the right operand is zero, a System.DivideByZeroException is thrown. If the resulting value is too large to represent in the decimal format, a System.OverflowException is thrown. If the result value is too small to represent in the decimal format, the result is zero. The scale of the result is the smallest scale that will preserve a result equal to the nearest representantable decimal value to the true mathematical result. Decimal division is equivalent to using the division operator of type System.Decimal.
For an operation of the form x % y, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. The predefined remainder operators are listed below. The operators all compute the remainder of the division between x and y. · Integer remainder: int operator %(int x, int y); The result of x % y is the value produced by x – (x / y) * y. If y is zero, a System.DivideByZeroException is thrown. If the left operand is the smallest int or long value and the right operand is -1, a System.OverflowException is thrown. In no case does x % y throw an exception where x / y would not throw an exception. · Floating-point remainder: float operator %(float x, float y); The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaN’s. In the table, x and y are positive finite values. z is the result of x % y and is computed as x – n * y, where n is the largest possible integer that is less than or equal to x / y. This method of computing the remainder is analogous to that used for integer operands, but differs from the IEEE 754 definition (in which n is the integer closest to x / y).
· Decimal remainder: decimal operator %(decimal x, decimal y); If the value of the right operand is zero, a System.DivideByZeroException is thrown. The scale of the result, before any rounding, is the larger of the scales of the two operands, and the sign of the result, if non-zero, is the same as that of x. Decimal remainder is equivalent to using the remainder operator of type System.Decimal.
For an operation of the form x + y, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. The predefined addition operators are listed below. For numeric and enumeration types, the predefined addition operators compute the sum of the two operands. When one or both operands are of type string, the predefined addition operators concatenate the string representation of the operands. · Integer addition: int operator +(int x, int y); In a checked context, if the sum is outside the range of the result type, a System.OverflowException is thrown. In an unchecked context, overflows are not reported and any significant high-order bits outside the range of the result type are discarded. · Floating-point addition: float operator +(float x, float y); The sum is computed according to the rules of IEEE 754 arithmetic. The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaN’s. In the table, x and y are nonzero finite values, and z is the result of x + y. If x and y have the same magnitude but opposite signs, z is positive zero. If x + y is too large to represent in the destination type, z is an infinity with the same sign as x + y.
· Decimal addition: decimal operator +(decimal x, decimal y); If the resulting value is too large to represent in the decimal format, a System.OverflowException is thrown. The scale of the result, before any rounding, is the larger of the scales of the two operands. Decimal addition is equivalent to using the addition operator of type System.Decimal. · Enumeration addition. Every enumeration type implicitly provides the following predefined operators, where E is the enum type, and U is the underlying type of E: E operator +(E x, U y); At run-time these operators are evaluated exactly as (E)((U)x + (U)y). · String concatenation: string operator +(string x, string y); These overloads of the binary + operator perform string concatenation. If an operand of string concatenation is null, an empty string is substituted. Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object. If ToString returns null, an empty string is substituted. using System; class Test The result of the string concatenation operator is a string that consists of the characters of the left operand followed by the characters of the right operand. The string concatenation operator never returns a null value. A System.OutOfMemoryException may be thrown if there is not enough memory available to allocate the resulting string. · Delegate combination. Every delegate type implicitly provides the following predefined operator, where D is the delegate type: D operator +(D x, D y); The binary + operator performs delegate combination when both operands are of some delegate type D. (If the operands have different delegate types, a binding-time error occurs.) If the first operand is null, the result of the operation is the value of the second operand (even if that is also null). Otherwise, if the second operand is null, then the result of the operation is the value of the first operand. Otherwise, the result of the operation is a new delegate instance that, when invoked, invokes the first operand and then invokes the second operand. For examples of delegate combination, see §7.8.5 and §15.4. Since System.Delegate is not a delegate type, operator + is not defined for it.
For an operation of the form x – y, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. The predefined subtraction operators are listed below. The operators all subtract y from x. · Integer subtraction: int operator –(int x, int y); In a checked context, if the difference is outside the range of the result type, a System.OverflowException is thrown. In an unchecked context, overflows are not reported and any significant high-order bits outside the range of the result type are discarded. · Floating-point subtraction: float operator –(float x, float y); The difference is computed according to the rules of IEEE 754 arithmetic. The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaNs. In the table, x and y are nonzero finite values, and z is the result of x – y. If x and y are equal, z is positive zero. If x – y is too large to represent in the destination type, z is an infinity with the same sign as x – y.
· Decimal subtraction: decimal operator –(decimal x, decimal y); If the resulting value is too large to represent in the decimal format, a System.OverflowException is thrown. The scale of the result, before any rounding, is the larger of the scales of the two operands. Decimal subtraction is equivalent to using the subtraction operator of type System.Decimal. · Enumeration subtraction. Every enumeration type implicitly provides the following predefined operator, where E is the enum type, and U is the underlying type of E: U operator –(E x, E y); This operator is evaluated exactly as (U)((U)x – (U)y). In other words, the operator computes the difference between the ordinal values of x and y, and the type of the result is the underlying type of the enumeration. E operator –(E x, U y); This operator is evaluated exactly as (E)((U)x – y). In other words, the operator subtracts a value from the underlying type of the enumeration, yielding a value of the enumeration. · Delegate removal. Every delegate type implicitly provides the following predefined operator, where D is the delegate type: D operator –(D x, D y); The binary – operator performs delegate removal when both operands are of some delegate type D. If the operands have different delegate types, a binding-time error occurs. If the first operand is null, the result of the operation is null. Otherwise, if the second operand is null, then the result of the operation is the value of the first operand. Otherwise, both operands represent invocation lists (§15.1) having one or more entries, and the result is a new invocation list consisting of the first operand’s list with the second operand’s entries removed from it, provided the second operand’s list is a proper contiguous sublist of the first’s. (To determine sublist equality, corresponding entries are compared as for the delegate equality operator (§7.10.8).) Otherwise, the result is the value of the left operand. Neither of the operands’ lists is changed in the process. If the second operand’s list matches multiple sublists of contiguous entries in the first operand’s list, the right-most matching sublist of contiguous entries is removed. If removal results in an empty list, the result is null. For example: delegate void D(int x); class C class Test cd3 = cd1 + cd2 + cd2 + cd1; // M1 + M2 + M2 + M1 cd3 = cd1 + cd2 + cd2 + cd1; // M1 + M2 + M2 + M1 cd3 = cd1 + cd2 + cd2 + cd1; // M1 + M2 + M2 + M1 cd3 = cd1 + cd2 + cd2 + cd1; // M1 + M2 + M2 + M1
The << and >> operators are used to perform bit shifting operations. shift-expression: If an operand of a shift-expression has the compile-time type dynamic, then the expression is dynamically bound (§7.2.2). In this case the compile-time type of the expression is dynamic, and the resolution described below will take place at run-time using the run-time type of those operands that have the compile-time type dynamic. For an operation of the form x << count or x >> count, binary operator overload resolution (§7.3.4) is applied to select a specific operator implementation. The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator. When declaring an overloaded shift operator, the type of the first operand must always be the class or struct containing the operator declaration, and the type of the second operand must always be int. The predefined shift operators are listed below. · Shift left: int operator <<(int x, int count); The << operator shifts x left by a number of bits computed as described below. The high-order bits outside the range of the result type of x are discarded, the remaining bits are shifted left, and the low-order empty bit positions are set to zero. · Shift right: int operator >>(int x, int count); The >> operator shifts x right by a number of bits computed as described below. When x is of type int or long, the low-order bits of x are discarded, the remaining bits are shifted right, and the high-order empty bit positions are set to zero if x is non-negative and set to one if x is negative. When x is of type uint or ulong, the low-order bits of x are discarded, the remaining bits are shifted right, and the high-order empty bit positions are set to zero. For the predefined operators, the number of bits to shift is computed as follows: · When the type of x is int or uint, the shift count is given by the low-order five bits of count. In other words, the shift count is computed from count & 0x1F. · When the type of x is long or ulong, the shift count is given by the low-order six bits of count. In other words, the shift count is computed from count & 0x3F. If the resulting shift count is zero, the shift operators simply return the value of x. Shift operations never cause overflows and produce the same results in checked and unchecked contexts. When the left operand of the >> operator is of a signed integral type, the operator performs an |
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