2.Typed vs untyped Field-Symbols
如果你在源程序中指定了类型化的field-symbols，那么ABAP/4编译器能够更好的对代码进行优化
FIELD-SYMBOLS: <F> TYPE ANY.
DATA: I1 TYPE I, I2 TYPE I.
ASSIGN I1 TO <F>.
I2 = <F>.
FIELD-SYMBOLS: <I> TYPE I.
DATA: I1 TYPE I, I2 TYPE I.
ASSIGN I1 TO <I>.
I2 = <I>.
DATA: I1 TYPE I, I2 TYPE I.
ASSIGN I1 TO <F>.
I2 = <F>.
FIELD-SYMBOLS: <I> TYPE I.
DATA: I1 TYPE I, I2 TYPE I.
ASSIGN I1 TO <I>.
I2 = <I>.
五、If, Case……
1.If vs. Case
Case语句比IF语句更清晰并且稍微快些
2.Comparison of I and C
C和C类型比较 比 C与I比较的速度更快
3.While vs. Do
While语句比Do-Exit语句更容易理解，并且执行的更快
4.Case vs. Perform i Of ...
