TheSwiftProgrammingLanguage(Swift2.1)第248页的注释解释了以下内容:Globalconstantsandvariablesarealwayscomputedlazily,inasimilarmannertoLazyStoredProperties.Unlikelazystoredproperties,globalconstantsandvariablesdonotneedtobemarkedwiththelazymodifier.Localconstantsandvariablesarenevercomputedlazily.摘自:AppleInc