通常带有“自然要发生”的含义,因而不包含“意愿”、“意图”等情态意义。
I shall be writing to you soon.
表示将来某一时刻或时段里的正在进行的动作;表示将来某一时刻之前已完成的动作便可用“will/shall +不定式完成体”
I will be working in Beijing during May.
You will have completed the course by this time next year.
表示某一已经开始的动作到将来某一时间仍在进行---“will/shall+不定式完成进行体”
If it rains again tomorrow, then it will have been raining for a solid week.
“will+不定式进行体/不定式完成体/不定式完成进行体”,一定语境下,仅表示说话人的揣测。
Hurry up. They will be waiting.